The world's been hit with an apocalyptic event, and humans are forced underground for survival inside large bunkers suited to house a couple thousand people. The bunkers are well supplied with modern technology, but aren't fully self sustaining. Over time, the need for these bunkers to trade and connect becomes evident. However, there are some obstacles in their way, mainly:

  • The world above is hostile, and with their current resources and technologies, it's unlikely a group of people would survive more than a couple of weeks outside.
  • They know there are other bunkers within the two week trek, but have no idea where other settlements are.
  • They can create simple tools like compasses and other navigation tools, but lack the ability to create more advanced things like vehicles.

Here are some other factors that might help in answering the question:

  • The world above is a hostile due to an unnatural Ice Age and constant severe storms, settling/surviving above would take too much energy, and reaps little benefits.
  • The settlements are powered by solar arrays supplemented by natural gas.
  • They have old world walkie talkies, but no radios and not enough knowledge to make those walkie talkies into anything more than what they're intended for (two way, short ranged communications)

With that in mind, is there a way for them to find each other, short of brute forcing and mapping out everything? and, more importantly, how do they establish trade that is safe?

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    $\begingroup$ If they have no idea where other bunkers are then there's a high probability that there isn't one within two weeks walk, so the whole thing is moot. You have to start with a legend of where one might be within range to get them searching. $\endgroup$
    – Separatrix
    Commented Jul 5, 2017 at 14:43
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    $\begingroup$ Do the bunkers need to hide from the outside world? Are there roving bands of pirates/looters? Or is it safe to leave a trail of breadcrumbs back to the bunker? $\endgroup$ Commented Jul 5, 2017 at 14:47
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    $\begingroup$ en.wikipedia.org/wiki/Smoke_signal - because you have solar power (that needs repairing and deicing if the weather is unfriendly) I assume they get to the surface sometimes. Oh btw, why are they not all dead from starvation? $\endgroup$
    – Raditz_35
    Commented Jul 5, 2017 at 14:56
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    $\begingroup$ There's a fatlal logic flaw here. If they don't know of the existence of the other bunkers, how do they know they need to trade with them? I mean Britain didn't push its trade routes into Asia because they knew how badly they needed tea. They had no want for tea, as they had no idea it existed. $\endgroup$ Commented Jul 5, 2017 at 15:59
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    $\begingroup$ severe storms and ice age <> solar panels. also, you'll have to come up with a really good reason why those bunkers shouldn't be equipped with short wave radio. That's the first thing anyone building a bunker will want to put in, staying in contact is a basic instinct. $\endgroup$
    – ths
    Commented Jul 6, 2017 at 11:50

11 Answers 11


It seems odd that an organization would set up multiple 1000 bed bunkers and not provide some method for them to contact each other. So any search for other bunkers should start by a thorough review of whatever documentation and paper work already exists within your current bunker.

If you find no clues there, your best first step would be to increase the visibility of your bunker. Build a tower and paint it orange. Start and maintain a signal fire. If there is a loadspeaker system or air-raid siren on the bunker complex, use it periodically such as at dawn and dusk. These actions will serve two purposes...

  • They will help your search parties find their way home at the end of each foraging mission.
  • They will make it easier for other bunker's search parties to find you.

Now all you need to do is start a methodical search of the area within one week of your base. Have your searchers keep their eyes open, looking not only for other bunkers but for radios, search-lights and other technical items which would facilitate communication. Also have them mark your territory, leaving spray painted messages and arrows everywhere.

If the weather is so bad that there is no threat of roving bands and pirates, then it is safe to advertise your bunker's presence and hope that other bunkers are doing the same.

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    $\begingroup$ The OP makes no mention of a central organization that was responsible for the construction of the bunkers. These could be privately-run, independent colonies, meaning there may not be any person or document that could tell you where the other bunkers are. $\endgroup$ Commented Jul 5, 2017 at 17:48
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    $\begingroup$ Which is why I didn't end my answer after the first paragraph. $\endgroup$ Commented Jul 5, 2017 at 17:55
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    $\begingroup$ @NuclearWang it is highly unlikely that man(alien)-made bunkers, even if done by the private sector and by different authors, would not have a method of comunication, or at least a protocol to follow, a map indicating the n closest other bunkers, etc. It could be that they were all built in a hurry, but the OP should make that clear otherwise the story would not be consistent, IMHO. $\endgroup$ Commented Jul 6, 2017 at 9:32

There are several methods for location depending on your world...


If your world's weather doesn't prevent walkie-talkies from working, then they can try to use those for location of other shelters. If a signal is received, they can then use triangulation to determine a location. It's a trivial task to set up. The biggest limitation of this method is walkie-talkie range. While they often publish ranges of up to 50 miles, a quick Google search of product reviews shows the best non-commercial/non-military grade units usually max out at around 2 miles in real-world use. Obviously, military-grade units should have better range and might therefore be more practical. The lack of interference from other radio sources may help, too.

If you upgrade your walkie-talkie radios to CB radios, the range can be increased higher. Or switch them to short-wave radios and the range can be quite far -- line of sight at a minimum.

Though adverse weather will reduce your radios' ranges. This is probably the weakest method, though keeping a radio channel open at the home base "just in case" can help.


If your shelters want to be found, they can plant "flags" to help others find them. Signs at set distances pointing the way, high enough to be seen above any trees, etc. would work well for this. Think of things like billboards where the shelter paints "shelter XYZ is 2 miles south" or provides compass headings. Low-tech and easy. If billboards won't work, ground markers will. Teams, over a period of time, can build markers as simple as large arrows made from rocks pointing toward their home shelter.

Signal fires

The shelter can gather brush or use their natural gas reserves to light signal fires. The bigger the fire, the further away it can be seen. If the wind isn't high, then smoke can also be seen and tracked for miles around during the day. At night, the fires would be visible at a distance. This also would be a good method to dispose of any non-recyclable material the shelter consumes.

  • $\begingroup$ This seems like a very good idea, especially using triangulation to contact one another. $\endgroup$ Commented Jul 5, 2017 at 20:25
  • $\begingroup$ I think you are a little pessimistic about triangulation. A walkie talkie signal can be turned into comprehensible speech at a range of a few miles, it can be detected further away than that. Triangulation just needs detection. $\endgroup$ Commented Jul 6, 2017 at 17:25
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    $\begingroup$ My pessimism is more about range and the area to cover than anything else. It would be a useful tool, but I wouldn't want it to be my ONLY tool. $\endgroup$
    – CaM
    Commented Jul 6, 2017 at 17:26

What you describe sounds like climbing mountains or travel through deserts. Hence the best solutions is to behave like you're climbing a mountain or you're travelling in a desert.
You must create caravans that travel short distances and create a commercial post, in your case a new bunker or a shelter, or using the analogy of a mountain, an encampment that is constantly supplied by sherpas. Each shelter should announce its location to the surrounding area.
After some time a map will be created showing the bunkers and shelters, good location shelters will turn into permanent settlements, like commercial posts between two bunkers.

  • $\begingroup$ And the commercial posts can turn into new bunkers! $\endgroup$ Commented Jul 6, 2017 at 4:56
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    $\begingroup$ How do you get somewhere one month away if you can only travel two weeks at a time? Two weeks at a time. $\endgroup$
    – Mazura
    Commented Jul 7, 2017 at 9:53

Allow me to suggest that the same technology that was discovered back when Steam engines ruled could be co-evolved here without a stretch of credibility: namely short wave radio. It has the advantage of being able to reach ( as long as ionosphere is undisturbed) virtually the whole world, it can be produced by 1890's -era hardware technology and hand-manufacturing techniques. A simple above-ground antenna could be constructed over time, negating the need for long term surface exposure. When combined with a simple "morse" code or its equivalent, short wave radio would allow your subsurface refugees the same as we have today with SETI and other extraterrestrial communications, we broadcast, we listen, we hope.


This is so simple that this answer will probably end up on the low content and length queue.

They would use seismophones, seismometers and seismographs to detect the underground activity of other bunkers. It would be easy to build a seismometric communications. Any heavy machine banging away at a large piece of rock or metal with a hammer or stamping tool, could send vibrations through the Earth's crust.

Then it's only a matter of digging in the right direction. Eventually a system of tunnels will connect the bunkers together.

  • $\begingroup$ The question seems to assume the bunkers are up to two weeks travel time apart. that means 150km or more. Digging those tunnels would be some really massive endeavour. $\endgroup$
    – Burki
    Commented Jul 6, 2017 at 11:31
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    $\begingroup$ @Burki. You mean they're let a little thing like that stand in their way!? These days people living in bunkers aren't like the people lived in bunkers back in the day. $\endgroup$
    – a4android
    Commented Jul 6, 2017 at 11:59
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    $\begingroup$ Those tunnels would be a massive undertaking even with a pre-apocalypse economy and technology. $\endgroup$ Commented Jul 6, 2017 at 17:31

For Trade:

They can create simple tools like compasses and other navigation tools, but lack the ability to create more advanced things like vehicles.

I assume you mean like modern vehicles such as cars, planes, etc.

Rail or even trade routes is out because of the shifting icy landscape. Air travel is out because of the storms, although if there are seasons of calm, it might be possible to travel great distances using hot air balloons... but the volume of trade would be limited by weight.

What remains are overland caravans using a sled and some animal to pull it. Even if its a human powered sled, transporting goods on a sled is something that should be considered minimum level technology.

For Communication:

For the purpose of finding more settlements, an air balloon should be able to identify new bunkers by spotting their solar panels. A quick landing could verify whether it is occupied (and could provide a new "colony" for overpopulated settlements). Actually any active settlement would require regular cleaning of the solar panels, so it should be pretty obvious from the air at a settlement is occupied.

The air balloon crew could also use the radios to reach out... and be the mail delivery service of the new world.

If the settlements are in previously urban areas, there should be plenty of electric and telephone wires (non-fiberoptic) that SHOULD be relatively resistant to weather. Put together crews to splice wires from all of the unusable raw materials and create a telephone between settlements. Old style manual operator switch boards would be needed to replace the modern computer switches, plus power to the telephone wires and you can have a simple hardwired communication system.


These are all underground bunkers, most likely they will leave in sensors that will detect earthquakes and such. I suggest turning up the sensitivity to detect more subterranean activity or creating something that can be sensed by the other bunkers, simple explosives should be effective.

going the simple explosive route the bunker that starts this can send Morse code to communicate. This will be visible to every bunker around, so there will be no secret meetings.


They could meet by pure chance on a foraging mission.

You could increase that chance by having a landmark near both of them, maybe the bunkers were built in a circle around a city, or near a lake and they meet in the city by chance. Or they see evidence of others when they visit and eventually track them down using good old fashion tracking skills.

In terms of 'how they know that trade is safe': This way they could trade in the city, rather than letting the others know where their bunkers are, and build trust over time.

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    – Secespitus
    Commented Jul 6, 2017 at 11:02

The obvious answer is they trade with people, who trade with other bunkers. Hardy caravans of stoic outsiders who are prepared to run goods between settlements - both existing topside ones and the bunkers - will gradually find bunkers as they travel and explore.

But you need to attract the trade caravans. Once they've discovered you, why would they bother to use you as a trade node? One immediate idea is that a self sufficient bunker must be able to produce food, probably growing fruit and veg -this might be hard outside in your blasted icy wasteland so the bunkers have something the outsiders want.

However, you want the bunkers to trade with each other, so they need to need things other bunkers have and be able to produce surpluses that other bunkers need. Requiring trade is easy, if a bunker's hydroponics packs up then they need food. But you need to find something they have - and more importantly, produce - in surplus that another bunker would require? I'd suggest you should manage these inter-dependencies with different systems breaking down in different bunkers. Say, one struggles to grow food, another struggles to pump up natural gas.

Then you have:

  • Bunkers are discovered.
  • Trade goods can travel between them.
  • Trade is required/desirable.


Assuming that the duration of their stay underground hasn't caused any mutations or lost of eye sight and whatnot. I would start by addressing the current status quo. Why has it shifted into a need to reach out from the safe zone, or more solidly, why is the safe zone no longer safe. This would most likely come about during a town meeting or similar.

Plan, vote, execute. In a modern society to get anything done there is a committee who delegates and ultimately decides on the course of action, thusly creating the Plan. A vote on which of the committees ideas holds the best weight in the eyes of the people. They would focus on these 3 topics:

  • Method - most logically by foot, protected by clothes, carrying maybe a bedroll or tent. This is because the people have forgotten to pass down rounded education to their children and thusly now only have limited intellect.

  • Explore - teams of explorers, if possible multiple teams are best. Send one up, send one through. Have an "air team" and a "cave team" Where they each struggle differently in their own hostile environments. But when out in the real world explorers should be building waypoints or emergency bases. Places to run to in extreme situations when you can't get back to base. These waypoints could also eventually create a grid of safe spots used to travel and trade, possibly, as well as map markers. Because knowledge is power especially when passed down.

  • Educate - at this point education needs to be emphasized as lost intelligence is the worse thing any society can deal with. Schooling should be continued or emphasized as extremely valuable for survival. Especially by the experienced to the young.

The most logical path is explore ALL avenues and expect NONE to flourish. Do not put all eggs in one basket. I would hope the committee would agree that sending 2 or 3 or more search parties would be best. One via external extreme hostile environment, one via caves and tunneling, and more in other directions if possible. Small teams of 5 to 10.

That said, the cave exploration would stop quickly once they reach a material harder than handtools will allow them to cut through. It would take decades to tunnel with handtools any real or usable distances. Explosives would speed things up but could cause more damage than help.

Luck would have 1 team find an underground river complex, a reason to send multiple exploration parties. Rivers are like roads and can be utilized for travel and trade. Obviously they would need to be able to build boats.

Luck would also have a 2nd team find old not yet collapsed abandoned subways, or sewers if near a major city. Using the rails or water to carry trade goods.

Luck would also have a 3rd team find pre-existing tunnels within the natural gas mines. Maybe stumbled upon once depleted.

Logically though no one would return without a plan.

All of that said is why I, as a member of that important committee, wouldn't put all my eggs into one basket. Think of it like this, its easier to hit an unknown target in pitch darkness with a shotgun rather than with a handgun.


How would purely underground settlements find and trade with each other?

I have had the same idea several years ago.And it is a great track to follow! My idea was about a fully ice covered earth (Snowball Earth). I mean no way out of the the underworld! Underground settlements find and trade with each other was a matter of survive or not.An army of diggers was the story focus.Forget radio technology, no way it works inside hard rock. Sound is your friend. Inside rock sound goes further and goes much faster. Like World War II the best submarine tool for seeking by friends/foes was a man ears, the hidrophone operator ears.


Captured underwater noise was transmitted directly from the hydro-phone to operator's ear-phones. The each ear-phone was connected with the one hydro-phone. By strength of noise in particular ear-phone, the operator detected from which side (starboard or port side) the noise coming. The ship turned round until the noise was now same in booth operator's ear-phones. When the noise was same in the both ear-phones the ship's crew knew that the ship is on course to the source of the noise, i.e. to the submarine. Range of that first underwater sound detectors was up to 4 nautical miles, accuracy was from 15 to 20 degrees.

I dont finish my tale because where I live it is impossible to publish. But I think it could work great for a length novel. Good luck.


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