This dungeon/ruin has been known to locals for ages. Why would it still have undiscovered portions ripe for looting?

Question

There's a ruin of an ancient structure built by an old powerful civilization thousands of years before. Nearby is one of the fresher cities of this world, currently undergoing an industrial revolution. The ruins are known to the denizens of the city, and it isn't especially hard to get to them from the city. By the current time, the outermost structure is almost mundane to the locals, and everything of value that could be stripped down was stripped down long ago, so they don't even think of it as something important. They think of it as just an old pile of rocks, and not even a particularly large one at that either (No bigger than a medium medieval castle).

The question: How can this structure have new untouched sections remain that nobody else had even suspected existed before? I'll accept both the external and internal reasons for this.

The ruins don't have any deterrents like dangerous monsters or mechanical/magical traps, since those would be presumed to be killed and destroyed in the prior centuries, even if there were any (in the known section, at least).

Answer 1

The explorers find a small vertical shaft that seems to go down a long way. The locals have dismissed this as a well or garderobe and so it has not been explored but it was actually a ventilation shaft that is the only intact path to a much deeper level of the structure, the main path having been blocked off by seismic activity eons ago. The explorers may have to bring mining technology to pump out accumulated water and clear the now foul air before being able to use this route.

Answer 2

Real history example

The ruins of Troy had been know to the locals for ages. Of course they didn't know they were ruins of Troy, because they had no idea about ancient Troy. They were Turks, and rural Turks didn't read Homer. They called it Hisarlik (Turkish for "fortress") and during the centuries they happily reused the stones to make their houses.

Eventually, no stone remained on the surface of the tell, one mound of ancient debris among many such semi-artificial mounds dotting the landscape in a region where history is measured in millennia.

Then an American named Frank Calvert came, in 1847, and bought 2000 acres of land including (part of) the mound of the Fortress. He was a self-educated amateur archaeologist, and did some digging; he found some artifacts of Hellenistic age, and became convinced that deep below must lay buried a splendiferous ancient city.

And he called Heinrich Schliemann. Schliemann, like Calvert, was a self-taught amateur archaelogist. The difference was that Schliemann was rich. By the standards of 19th century rural Turkey, Calvert was rich too, but Schliemann was rich by European standards. He hired a small army of workers, and began a systematic exploration of the tell in 1870.

In three years he dug layer below layer, discovering the ruins of nine cities buried one on top of another. And on 27 May 1873 he struck gold.

^{Left: Schliemann's Greek wife, Sophia, wearing the jewels of Helen of Troy. Photograph from 1874. Right: the large diadem with pendants, exhibited at the Pushkin Museum in Moscow. Photograph by Szilas, available on Wikimedia. Public domain.}

The so-called treasure of Priam contained (list from Wikipedia):

• a copper shield.
• a copper cauldron with handles.
• an unknown copper artifact, perhaps the hasp of a chest.
• a silver vase containing two gold diadems (the "Jewels of Helen"), 8750 gold rings, buttons and other small objects, six gold bracelets, two gold goblets.
• a copper vase.
• a wrought gold bottle.
• two gold cups, one wrought, one cast.
• a number of red terracotta goblets.
• an electrum cup (mixture of gold, silver, and copper).
• six wrought silver knife blades (which Schliemann put forward as money).
• three silver vases with fused copper parts.
• more silver goblets and vases.
• thirteen copper lance heads.
• fourteen copper axes.
• seven copper daggers.
• other copper artifacts with the key to a chest.

Part of the treasure is nowadays located at the Istanbul Archaeology Museum. The bulk of the treasure went first to the Royal Museums of Berlin, and in 1945 it was taken by the Russians; it is now at the Pushkin State Museum of Fine Arts in Moscow.

Heinrich Schliemann went on to make other unexpected discoveries, including the famous gold mask of Agamemnon at Mycenae.

Another great story is the discovery of the tomb of Tutankhamun by Howard Carter in 1922; or the lucky fall of a young Roman into a mysterious grotto on the Esquiline hill, in the 15th century, discovering the remains of Nero's Domus Aurea, and Raphael and Michelangelo crawling underground to copy the wondrous frescos; but those remains for another time.

Answer 3

Earthquake!

Your character is in the ruins when an earthquake occurs! Dangerous, scary stuff! Of course the earthquake could have happened the week prior and then your character shows up, but how exciting is that?

In any case, the quake moves things. Walls collapse, floors shift. Secret passageways, hidden rooms and tunnel entrances are revealed. I like the idea that earthquakes have happened in this part of the world before, and perhaps some of the "hidden" rooms were not intentionally hidden by the builders, but wound up that way as a result of an ancient megaquake that caused the building to be deserted as unsound.

Answer 4

Easy

The Ancient Ruins are a Labyrinth

The naive townsfolk think that they have found everything there is to know about this place, but they haven't even scratched the surface of what this complex really is.

The ignorant tomb raiders thought that this place only had one floor. They robbed the first floor until there was nothing left, never realizing that there was more beneath it.

This was intentional on the designer's part. They had lots of important items they wanted to keep hidden from prying eyes, and they were paranoid at the prospect that anyone would find them, so they set out to make the layout of this building as complicated as possible. They took the secret of how to navigate this place to their grave.

Despite looking like a simple structure at first, this building goes deep into the ground and has countless hidden tunnels as well, none of them in obvious places. They were so cleverly disguised that no one who passed by even realized there might be a secret path there in the first place. Why would they even bother to look?

This is the main reason why so many treasures remain unplundered and unsullied by mortal hands or eyes. Once the most important artifacts were stolen, people lost any interest in this place. They thought they mapped everything out and checked every corner, but they were only scratching the surface.

Not only are there more floors that they could have discovered, but there are dozens they have yet to touch. Thousands of rooms are lying hidden behind fake walls, secret trap doors, and tiny crawl ducts that no one ever bothered to check.

It's easy to miss this kind of thing, but the designer of this place wanted people to get as lost and disoriented as physically possible. They put all their hard work into concealing the truth.

Anyone smart enough to actually get into the more inner chambers of the building has found themselves way in over their heads. These areas were designed to be tough to enter and even tougher to exit. You might be able to open the doorway to Floor Two by sheer luck, but you'll never be able to get out without the proper code. You don't even need traps or monsters to guard the entrances and exits. An unbreakable stone wall blocking the way and endless caverns are enough. If you don't know what you're doing or where you are going, the entrance will lock behind you and you will be stuck in a lightless place until you eventually succumb to thirst or starvation, whichever comes first.

Just when you think the paths will come to an end, and you've finally found your way out, the maze just keeps going and going.

Exploring This Place Seems Futile

Why would anyone want to visit a place that has already been explored and has no treasure to offer?

This is one of the main reasons why people tend to stay away from it. They think it's already been pilfered, so what would be the point of going anywhere near it?

People tend to go exploring for two reasons. They either think there is something worthwhile in the location, or they are in it for the pure thrill of adventuring to an unknown place.

If there is no treasure left to steal, and the rumor that has been spread for years is that there is nothing good remaining, then no one would bother going there.

Have this building be protected by its sheer mundanity. As far as people are concerned, it has nothing left to give them. It's not an exciting destination to visit, it's a boring, dusty ruin that everyone wishes was demolished. It's just an eyesore.

It's called "hiding in plain sight". The more unassuming the place seems, the better hidden the artifact will be.

In fantasy, we tend to expect the McGuffin to be lying on a pedestal in some massive temple, surrounded by hundreds of powerful guards.

The guards might be a good idea, but if you really want to hide something, you wouldn't hide the McGuffin in someplace grand and luxurious. Hide it in a place so unsightly and boring it never occurred to anyone that it would be there.

Lots of Fakeouts and Lots of Fake Rewards

Have this be a reoccurring theme with this ancient civilization.

They love making people think they have found everything, all while they silently laugh in their graves because they know you walked out with something worthless compared to what was hidden a floor below you.

Like I was saying before, this place has dozens of floors underneath the main one.

The first one is designed to look like it is the only one, and countless valuable treasures are dotted along the place to make it more convincing.

Gold, silver, ancient weapons, and so on, are on every corner of the room and surrounded by traps, but all of that stuff is either a bunch of decoy goods or plain worthless compared to what this place was intended to hide.

This ancient civilization was rich. Gold, silver, and jewels were like dirt to them. Enchanted swords and spellbooks were everywhere. So they just shove all the worthless junk on the top floor to trick people into taking that. Once their greed is satiated and they find nothing else, they leave and think that is all.

Little did they know there were fire-shooting Gauntlets on the floor just below them. The designers laugh at the ignorance of the thieves.

Oh no, the thieves found the Fire Gauntlets? Sike. The real gauntlets were in another room. Those are fakes that scorch the user's bobdy until they're nice and crispy.

A hundred years pass and someone finally manages to find the real Fire Gauntlets on the Second Floor.

Jokes on them. On the Third Floor, they could have gotten the Elixir of Life which cures all illnesses and grants immortality. But they can keep their silly gauntlets.

Would you look at that? Someone found the Elixir of Life! Good for them. They have now cured all illnesses and ushered in a new era of peace. Good thing they didn't find the Dark Amulet on Floor 4 or else they might have unleashed the demon prince hidden within it.

Meanwhile, on Floor X, a ridiculous distance below the surface of the planet, the last remnant of the ancient civilization is snickering to herself.

The rest of her civilization transcended space and reality. That's why they all left, but she's decided to stick around and mess with adventurers like the main character until the day the sun dies and the world cools over. It's fun.

Ten thousand years after this place was built, she's bored. The main character is the first one to show interest in the Ancient Ruins for ages, so she (or he or they, you pick) decides to break radio silence and decides to give the main character a hint of what is truly hidden beneath the surface.

This could be how the crux of the story begins. The character takes interest in these seemingly boring and mundane ruins, gets a hint from an outside force, and investigates to find there was far more to this place than anyone ever knew. They unveil secrets that have never seen the light in millennia.

Answer 5

Lore incorrectly describes the Ruin because the rivets were used as horsehoes

Absolutely, your idea of thieves taking relevant items is just like real life.

One proposal is that the ruin's shape is misunderstood, and the interior map of it has never been properly visualized. This is a variation of it was "hidden really well", "there was a secret door" combined with the fact that the clues themselves may be stolen over time which make the floor plan misunderstood.

Let us say that the treasures of the outer surface have been taken by several expeditions. The surface has been previously excavated numerous times with the legend being reinforced each time that there is nothing further there.

There is a burial mound called Sutton Hoo in Suffolk England that contained many treasures. Apparently it had been plundered since the 1600s various times, and it had never been understood as being a buried ship until the period of the Second World War. Each time people went to the mound in previous excavations, they removed some clues that would have helped other archaeologists from understanding it. The earlier explorers (thieves) did things like melt down the treasure or even use the ship rivets for horseshoes. They disturbed the ground by created "robbers trenches" that obscured everything. In 1938 the landowner, Edith Pretty, hired a local archaeologist to look at some mounds on her property previously thought empty. The archeaologist, Basil Brown who eventually found the ghost of a ship by digging a series of cross sections in the ground, by carefully excavating Sutton Hoo, he found many more artifacts, that are now thought to have been owned by a king of East Anglia. The discovery and the dig were the plot of a book and a movie.

A couple things for the Sutton Hoo story could be adapted to a ruin in an invented world. Here is what I think is applicable:

• myths and legends inaccurately say that all treasure has been taken
• local lore says the ruin is in one site, when in fact is in more than that one location
• Actual physical clues have been stolen
• The ruin's layout is misunderstood completely -it takes a new inventive approach to unearth further artifacts.

The treasures found by later excavation included a masked helmet and a sword.

Answer 6

Tech-dependent "secret door"

Other answers have suggested secret doors or massive excavations, and these are both very good reasons why the loot hasn't been found. However, we could also have a tech-dependent test. The classic example, readily usable here, is from 2001: the castle could have a powerful magnetic field emanating from one part of its cellars. The discoverer might simply be the first person who brought a magnetic compass to the ruins and noticed deviations. Rather than having to hire an army to excavate the entire castle, you might be able to reach a well-preserved entrance with a lone shoveller persisting through a few utterly miserable days of labor.

If you don't want to suffer through dialogue with Clarke fans, it might be better to use a different technological key. For example, the ruins might generate radio interference that the finder tracks down like the magnetic field. Maybe instead of digging for the secret, he tries to respond with his Morse code key. Though communication may not be achieved this way, the loud radio interference might advance a preexisting protocol that opens the silo doors and rewards the brilliant scientist with the enduring fame that comes from being the first person to fall to his death in an underground nuclear silo in two thousand years.

Speaking of nukes, the presence of the newly discovered Roentgen ray would be another way lead your society's explorers to the castle. They might notice film-fogging rays in a local waterway, and trace them back to a small rivulet of leakage from the site. This has the particular advantage that the original creators of the artifact might have avoided it, but scientists new to the wonders of radiation would be free to move onward, though some might have to take some time off for some troublesome ailments: nausea, burns, hair loss and so on.

Answer 7

The true entrances are kept secret by riddles and other non-lethal forms of separation. Perhaps even the doors are simply too well hidden for the locals to find.

If you do not want the characters to have to figure it out, give them a book or a scroll describing the way in.

Answer 8

The locals are aware of an underground lake, they are not aware of the water flow that maintains it as it's through gravel, not an open stream. There has been a shift in the drain, the lake is gone, exploring the old lakebed reveals it used to be more extensive until the water flow flooded part of it. Now the areas that were inaccessible (and thus unknown) are accessible.

Related possibility: Something happened upstream to divert the flow before it reached the dungeon in the first place.

Answer 9

It depends on how far you want to tip the scales between Believable and Magic. On the magic end, this happens in stories all the time. The protagonist is a descendant of ancient rulers that left the content millennia ago to escape a sacking, and this is the first time the family line, and in particular the family heirloom amulet that happens to be a magical key that the protaganist is wearing, has been in the city. Or he cuts himself on a piece of rusted metal and a blood drip happens to activate an ancient dna scanner.

The problem comes in figuring out why these right-at-the-surface entrances or technologies were never discovered. The site would have been used as a quarry, for ready-made stone blocks if nothing else, and anything at the surface would have been examined; an ancient indestructible monolith big enough to be an entrance would have been noteworthy.

So on the believable side, you're left very few possibilities, especially if you assume the locals are caught up with the rest of civilization, and aren't isolated primitives or something. It's just not believable that the ancient rune-covered doorway was never blasted open with dynamite or carted off intact to a museum (or to be used as the new local bank decorative wall to mount the ATM on), no matter how many vines cover it now. So, like the Troy example by AlexP, the dingus is just buried so deep under so many layers of conquest and rubble that no one has ever dug that far down before. Or what little of the ruins is actually explored has been so small and inconsequential that no one has really "explored" it at all. And even that kinda requires #1, or someone would have stumbled on something anyway. There are loopholes, though. If the ruins are at the top of a mountain or large hill, perhaps it turns out that most of the mountain or hill is actually catacombed with more ruin. But due to #1 and #2, no one knew. This allows a new opening in the side (a tree falls, exposing worked stone, or the back wall of a cave collapses into a room, etc) to offer a shortcut to the "deeper" regions without requiring months of investigation and digging. On flatter ground, a sinkhole, perhaps caused by the collapse of an ancient buried room, could do the same thing.

Or, maybe a mundane construction worker has been oversleeping and is working late to make up the hours after most everyone else has left. He's digging footings for a new sky-scraper hotel, which is well away from the ruin as far as everyone knows, when he breaks through into an ancient tunnel leading into the deeper section. He could just as easily be a rural farmer digging a new root cellar. If the tunnel is a one-off, such as an escape route used when the original castle was sacked, it may be just blind luck that he happens to dig where the tunnel came close to the surface.

I've heard that this kind of thing happens fairly regularly in places like Greece and such. There's so much civilization that all of Greece is built on top of ruins, and every new basement someone digs has a chance of unearthing a new set of artifacts. It's not too far fetched that one of them unearths something a lot more interesting than the normal pottery shards.

Answer 10

They have a private cemetery for the leaders.

Unknown to the locals, it was a tradition to have a secret graveyard for the lords of the castle, hidden away with special marks only the highest of priests knew behind hidden walls.

While these marks were long since lost to time, and the door long since broken, using modern archeological tools they have discovered a hidden void, much like the one in the great pyramid of giza. With the aid of the key and trusted archeological tool, the sledgehammer, they can reach the hidden graveyard of the dead kings, where the finest of loot was stored for their use in the afterlife.

Answer 11

It was well sealed

The ancients knew how to seal a tomb for eternity, in a way that as far as I know was actually invented by Hollywood for an epic set in ancient Egypt. (This method is about all I can remember of it). Above the corridor leading to the tomb, are huge blocks of stone supported on wooden props supported in turn on dry sand in cylinders with pottery seals. When the tomb is to be sealed, those seals (several levels below) are smashed, the sand runs out, and the huge block descends onto the floor leaving no way past it and no sign that it's not like all the other stone wall blocks that one has walked past to get to that point. Also, the design is such that there is an obvious corridor continuing at that point. This obvious corridor leads to decoy "tombs" stuffed with lesser valuables, sealed less effectively with conventional walls and curses whose power faded as popular beliefs changed, which over the centuries have been ransacked.

Modern technology brings something to reveal the hidden tomb. Maybe precise underground mapping. Maybe rock-penetrating radar. Maybe discovery of the under-corridor and somebody able to interpret the pieces of pottery, wood and surprising amounts of sand. Maybe somebody (mis?)understands meaning in a recently deciphered ancient text "that when the day of $long_forgotten_deity comes, the dead will rise from their tombs, and walk through their walls of rock as a bird flies through air".

You might also throw in some bats, and local folk knowledge which affirms that wandering around in caverns where bats roost tends to be bad for one's health.

Answer 12

The simple answer is that after a society becomes agricultural and no longer hunter-gatherers, they have much less time for exploration. They're still pre-modern, so you can't expect the kids to have much time to explore either... they're off pulling plows when the mule died or something.

Now, we do tend to see alot of myths and stories about hidden treasures in all cultures... so it's not as if the idea of there being stuff out there worth looking for is foreign to them. But think about the implications of that... they wouldn't be good stories if the people in them didn't find the hidden treasures. "And then Derpy Joe went out looking for the Lost City of Rubies, broke his neck, The End" isn't a compelling narrative.

The central conceit of the good stories is that the treasure is so well hidden/guarded, that only special people find them, no? This is the acknowledgement that hidden things tend to remain hidden, especially when everyone that was in on the secret is long dead.

Perhaps the biggest danger to your plot point is that if this stone was accessible, it would be very likely to be repurposed... it's much easier than quarrying new stone. But that's a minor nitpick and shouldn't detract from the story you're working on. Truly, if the ruins are extensive, then they might just give up on that after awhile, since the remaining stone eventually becomes too far to be worth the hassle, and especially so if the geography itself is difficult.

Answer 13

If your thousand year old civilisation was really advanced, you could take inspiration from "Horizon Zero Dawn".

Spoilers ahead:

The protagonist Aloy in this game lives in a world that is a blend of tribal/iron age technology combined with "magic-like" usage of broken down robotic machines.

She discovers and explores ruins of "old powerful civilization thousands of years" ago that are guarded/locked by several still working Artificial Intelligence clusters.

Exploring the ruins is helped by a device she found in one of the ruins as child. The device is a mix of an advanced mobile phone that is able to teach her and some kind of augmented reality thingy. It shows her information about what she can see and overlays this with her normal vision - accesssing her brain / visual cortex. Without this "trinket" she would be unable to comprehend certain riddles.

Some of those entrences only allow acces after she fixes some genetic scanning devices/data base - her genetic sequence is somehow fingerprinted and cleared for access - why is revealed throughout the game.

So essentially she needs this thingymabob to help her understand the technology her peers are unable to comprehend and allow her insights into puzzles / allow entrance into areas of ruins that are locked for others of her tribe.

Answer 14

I once read in a book by archaelogist Rodolfo Lanciani (1845-1929) that since the Renaissance every square foot in Rome had been excavated by looters and/or archaeologists at least once, and there were no more great discoveries to be made.

Caesar's Palace, the one in ancient Rome, is called The Palace of Domitian since it was mostly built during his reign in AD 81-96. It continued to be used more or less often by emperors and later by the Ostrogothic kings.

https://en.wikipedia.org/wiki/Palace_of_Domitian

Narses (478/480-557/74) reconquered Italy from the Ostrogoths in the 550s and resided in the imperial palace in Rome. And he might have been the last person to do so.

Emperor Constans II visited Rome for 12 days in 663, and might have stayed in the palace.

It is possible that the palace collapsed during an earthquake in Rome during the 800s. It was in ruins for a long time.

The Duke of Parma, who owned the Palatine Hill. had the palace excavated in the 1720s, I think, and stripped of its marble. And that might have been about 900 years since the palace collapsed into ruins.

During the excavations, Bianchini, the man in charge, fell through a floor and eventually died from his injuries. At the time it was believed he fell into a bathroom of the palace, but it is now known to be part of a previous Roman house on the site.

And I have read that later studies of the palace found a shaft leading downwards. It was believed at the time to be a dumbwaiter shaft to bring food up from the hypothetical lower kitchens. But I don't know if that is true, or if anyone ever found out where the shaft went to.

In December 2006, Italian archaeologists announced that an excavation under a shrine near the Palatine Hill had unearthed several items in wooden boxes, which they identified as the imperial regalia, possibly belonging to Maxentius.[24] The items in these boxes, which were wrapped in linen and what appears to be silk, include 3 complete lances, 4 javelins, what appears to be a base for standards, and three glass and chalcedony spheres. The most important find was a sceptre of a flower holding a blue-green globe, which is believed to have belonged to the Emperor himself because of its intricate workmanship, and has been dated to his rule.[25]

https://en.wikipedia.org/wiki/Maxentius#Discovery_of_Imperial_insignia

So those imperial treasures were not found for 1,694 years, if they were really buried when Maxentius was killed in 312.

I think that there are still some post Roman buildings on the Palatine Hill, and it has not been completely excavated.

The Roman emperors had their main palaces on the Palatine Hill, even before Domitian built his great palace there, and owned other houses, gardens, villas, and residences in Rome and nearby.

For example, Nero (r. 54-68) acquired several properties on the Esqaline Hill about a mile from the Palatine Hill. He also acquired property between the two hills and built an estate connecting them, which he called the Domus Transitoria.

https://en.wikipedia.org/wiki/Domus_Transitoria

During the great fire of Rome in AD 64, many buildings in Rome were destroyed or severely damaged, including much of Nero's Domus Transitoria.

According to Seutonius:

XXXI. In nothing was he more prodigal than in his buildings. He completed his palace by continuing it from the Palatine to the Esquiline hill, calling the building at first only “The Passage,” but, after it was burnt down and rebuilt, “The Golden House.” 600 Of its dimensions and furniture, it may be sufficient to say thus much: the porch was so high that there stood in it a colossal statue of himself a hundred and twenty feet in height; and the space included in it was so ample, that it had triple porticos a mile in length, and a lake like a sea, surrounded with buildings which had the appearance of a city. Within its area were corn fields, vineyards, pastures, and woods, containing a vast number of animals of various kinds, both wild and tame. In other parts it was entirely over-laid with gold, and adorned with jewels and mother of pearl. The supper rooms were vaulted, and compartments of the ceilings, inlaid with ivory, were made to revolve, and scatter flowers; while they contained pipes which (360) shed unguents upon the guests. The chief banqueting room was circular, and revolved perpetually, night and day, in imitation of the motion of the celestial bodies. The baths were supplied with water from the sea and the Albula. Upon the dedication of this magnificent house after it was finished, all he said in approval of it was, “that he had now a dwelling fit for a man.”

https://www.gutenberg.org/files/6400/6400-h/6400-h.htm#link2H_4_0007

And after the reign of Nero the Golden House was abandoned over time, and its buildings demolished, or filled with earth and rubble, and new buildings and streets built over them.

When a young Roman inadvertently fell through a cleft in the Esquiline hillside at the end of the 15th century, he found himself in a strange cave or grotto filled with painted figures.[8] Soon the young artists of Rome were having themselves let down on boards knotted to ropes to see for themselves.[15] The Fourth Style frescoes that were uncovered then have faded now, but the effect of these freshly rediscovered grotesque[16] decorations (Italian: grotteschi) was electrifying in the early Renaissance, which was just arriving in Rome.

https://en.wikipedia.org/wiki/Domus_Aurea#Rediscovery

It was claimed that Fabulus, or Famulus, the main artist decorating the Golden House, was so proud and successful that he painted wearing a toga, and certainly his style has been very influential during the last few centuries.

And in about 2014, another part of the Golden House was discovered:

Archaeologists were digging on an artificial terrace on the northeast corner of Rome's Palatine Hill when they found a round, 12-metre-high tower, with a large central pillar of four metres in diameter and 8 pairs of arches supporting two floors. Along the top of the upper arches, were lines of semi-spherical holes, filled with slippery clay – somewhat like the cavities that were used on large ships to contain primitive ball bearings, on which moveable platforms were mounted to transport heavy loads.

According to the team of archaeologists who uncovered the structure, the lines of cavities housed metal spheres that supported the revolving floor. At the bottom of the tower, they also found evidence of a mechanism had been built into the wall. Scientists said the calcite deposits on the surrounding walls were a result of the floor's constant movement. It might have also been powered by water channeled system of gears.

https://www.ancient-origins.net/news-history-archaeology/revolving-dining-room-emperor-nero-s-luxurious-palace-really-existed-001824

So I can find it easy to believe that after all this time, someone could find a little buried box full of jewels, or containing an interesting ancient papyrus or parchement, somewhere in Rome. Or in a fantasy story some magical ancient artifact.

So if some vast undergound complex was built by people who had powered construction and excavating equipement, arificial lighting and ventillation, etc. (or magical equivalents in works of fantasty) it could be incredibly vast and complex, and hard to explore for people with more primitive technology such as torches for light.

Thus hidden secrets and treasures might still there after centuries or millennia.

And possibly the underground chambers and tunnels were radioactive or poisonous, and everyone who entered them for centuries soon died, and their reputation has protected them from looting even after they became safe to visit.

Answer 15

Industrial revolution could be key point. That is improved tools like cutting tools. Knowing that these structures have been around for very long time they are likely made from good quality materials. Some concrete require diamond cutting to get through. Or otherwise is massive project to break.

So no one spend enough time to get through a blocked of wall. Or maybe they weren't strong enough to pull out blocking block or have suitable tools to mount necessary equipment. And thus such spot were generally forgotten even if relatively simple to identify. Now there is drills and saws or even cranks and other suitable tools to break through or pull it out.

Answer 16

Here's some of my ideas! I'll leave them sort of vague so you can expand on them yourself ^^

• The ruin still sees limited use in some areas, and may be controlled by a very strict group (gang, priests, gov., etc.) that prevents leaving the secure areas, or this limited use shows how dangerous the rest of the dungeon may be. This doesn't have to be deterrents like mnsters or traps, though! Old structures are super dangerous. Nobody wants to be in a place that could literally fall on top of them at any minute.
• Local legend about some terrible evil thing in the dungeon that may or may not actually be there.
• It was just hidden really well, and [character] has some way of knowing where the hidden parts were and how to get in.
• These parts were only just recently discovered. (this happens all the time IRL; both natural events and human intervention reveal hidden areas with all kinds of crazy stuff.)
• Magical nonsense. Some part of the ruin responds to mage blood or the right combination of magical woo-woo's or something.

Hope these help [: Good luck with your story!

Answer 17

It's out of the way

Yes, the locals know where it is. That doesn't imply that the dungeon is easily accessible; it could be at the top of the mountain, in the middle of a creepy-crawly filled rainforest, or any of a number of similarly inaccessible places.

As a result, while the locals know where it is, they don't usually bother to go there. Sure, you might find something of value there, but it's not worth the risk of getting killed.

Your intrepid adventurers, on the other hand, are in the business of going to dangerous places. Climbing sheer cliffs and hacking their way through rainforests filled with creepy crawlies is an everyday occurrence for them.

It's religiously significant

The locals know where the dungeon is and can get to it without getting killed. However, the site is holy; they're loth to even go in, let alone steal stuff, lest they incur the wrath of a deity.

Conversely, your adventurers have angered many deities in the past and will anger many more in the future. One more or less isn't going to make a difference.

It's historically significant

The locals can easily get there, and any religion which would take exception to trespassing has since been relegated to the history books. However, unlike your intrepid adventurers, they have enough reverence for the past that they aren't going to cast disintegrate on every wall which sounds even remotely hollow.

It's dangerous

Filled with pitfalls, dart launchers, pressure plates, grumpy eldritch abominations and rickety staircases, the dungeon has claimed the lives of many previous adventurers. Not having a death wish, the locals stay away.

Answer 18

Some further ideas here:

The main character knows something that the villagers don't

This could work well if you can connect it to an earlier adventure of the same character. Maybe they found an ancient text in another ruin that mentions a secret door to an underground section of the ruins, located where the shadow of the obelisk at the ruins falls at noon on spring equinox. The secret door is very non-obvious and was anyway long since covered by rubble and vegetation. Fortunately, the obelisk still stands...

The villagers do know about the undiscovered part but aren't telling

There is an altar to an elder god underground in the ruins. There is a cult in the village worshipping said god but they don't want to be discovered for some reason: maybe the god is really evil, or maybe it's a benevolent god but only the worship of one god is allowed in the country. After the main character arrives in town, they realize something funny is going on with the villagers and stealthily follow them to the ruins at midnight.

Answer 19

Read Deep Time -- Gregory Benford -- how humanity communicates across millenia

https://www.goodreads.com/book/show/2014020.Deep_Time

GB discusses among other things, how to mark a radioactive dump so that people don't want to go in.

Suppose you take a city, and surround it with a mile of stairs. But the stairs are the wrong size for easy use. You can travel them, but it's exhausting. The stairs form a maze. There are many entrances, but only one goes through to the city itself. 4 square miles split up into 10 foot wide passages gives you 2000 miles of maze.

Suppose that the outer architecture looks wrong: Asymmetrical. Nothing at right angles. Everything is coloured black and barf green.

Suppose the place smells of decay, carrion, death.

Suppose that the structure of the place creates it's own weather, so that it's always foggy, or always frosty.

Suppose there is a 20 mile radius circle with no living thing, no plants, no bugs. No water. You have to carry everything for your trip.

Suppose that this is a place that literally the sun does not shine. You walk across the boundary and you are in shadow. This keeps it cold.

Answer 20

It has been an unseasonably dry year and all the foliage in the area is brown and withered. Century old growths have receded to unprecedented levels, revealing aspects of the ancient ruins which were completely concealed before now. As a result of this newly exposed architecture, the overall shape of the ruin is easier to determine. The wall sets which point out obliquely from the previously overgrown center are obviously two compass point wings of a structure which probably also had wings aligned to the other two compass points, wings which, even now, are still concealed by brittle brown plant life.

The thinning of the cover and the revealed design of the ruined structure should provide your characters access to previously inaccessible chambers where un-plundered treasures await.

Answer 21

There was a secret vault in the City, mayhaps leading to another portion of it, but it was hidden even before the City's fall.

It opens only to a certain individual, or to a member of a bloodline, or to a wielder of a certain item. AKA the protagonist.