In the late 18th century, a strange project was proposed by a Dutch engineer regarding a certain English expedition. The British Empire held a vast amount of territories at this time and had much to protect. Certain members of the Royal Navy discussed whether it would be feasible to start and maintain a large-scale colony (Around 20,000 or more) in one of their outer territories to serve as a base for a military outpost. Britain had started many colonies before. However, this one was to remain utterly secret because of its military potential.

The purpose of this idea was two-fold: Operate a self-sustaining colony that can provide Britain with resources. And allow them to have a distant military outpost to protect their vast empire. One can operate in secret, including if necessary, from underground should the mainland or important territories fall under attack.

Not only would this colony have to be secret, but also able to withstand attacks and be well defended.

The engineer in question suggested an underground city or fortification of sorts. He was inspired by the underground networks and cities found in ancient cultures around the world. The man figured with the "modern" equipment and the vast resources at hand, the Commonwealth could surely utilize something similar.

The project began in the 1890s but picked up the pace from the early 1900s to before the war. By then, interest in the secret project had declined. Its high cost and the threat of war caused attention to be diverted elsewhere. Even though this outpost was designed to serve a military purpose, the Homeland and nearest territories were deemed of higher interest. And overtime the mining colony whose true purpose is only known to a few was abandoned.

As time goes on, the project was eventually disbanded, though most of the residents still remained long after they were abandoned. Being able to utilize the self-sufficient capabilities of the colony.

This develops into the main plot of the story.

My two questions are:

  1. What remote geographical location would serve best for this underground colony?

One that would both keep it secret up until modern times but also have the resources to be self-sufficient? (Portions of Australia wilderness or northern Canada seem as likely candidates)

Since this colony is built for military application, they likely would be somewhere near the coasts(but obviously this could cause water issues. However I thought perhaps water could be used as power for the colony's mining needs.)

  1. And realistically, where underground would the colony be built?

Obviously water-table and fault lines will play a role. (Though fault lines weren't discovered until 1915 if my memory is correct) I am aware of certain theories about the Earth's crust being "honeycombed". If so, perhaps a network of these large caverns would do. What about vacated magma tubes? Are there other natural structures that would provide a good area from which to house an underground colony?

Additional details:

  • The technology in question is early 20th century industrial equipment.
  • There is electricity involved.
  • The colony does have access to the outside world, but is designed to be able to live mostly underground.
  • The colony is nearly completely self-sufficient, including their own steel-making capabilities and people trained in weapons manufacturing
  • This is a large-scale colony growing to about 20,000 before being abandoned. And obviously larger in the years that followed.

Then :

  • The project is highly classified.
  • Sufficient funding is backing the project.
  • They have over two decades to complete it.

While I research various scientific studies, I am chiefly interested in robotics and astronomy. So, I am not up-to-date concerning much of geology. So please correct me if I have made any errors.

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    $\begingroup$ You seem to be missing the issue of lunch. How are they fed. Large supply lines are difficult to hide. The waste heat of such a colony will be very obvious once infrared observations are available, unless it is colocated with a known facility. $\endgroup$ May 13, 2022 at 22:53
  • $\begingroup$ I agree, Late Medieval is well before Hydroponics and LED lighting, torches of burning tallow aren't going to be enough to have all food production on-board. $\endgroup$ May 13, 2022 at 23:34
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    $\begingroup$ I planned to propose supply line issues in another question( I didn't know if it would be too much for one thread.) I'm glad you mentioned this. That is a very valid point. Logistics are vital for any large endeavor, especially colonization, as the people of Plymouth learned. Supplying the initial work crews could have been achieved with relative secrecy to foreign nations(There was no satellite imagery yet.) But local populations spotting supply lines would have been harder to convince. $\endgroup$ May 14, 2022 at 0:07
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    $\begingroup$ Can the place be disguised as a much smaller prison colony? $\endgroup$
    – user86462
    May 14, 2022 at 7:41
  • 1
    $\begingroup$ Yes. That would be the most logical cover story. Possibly some of the workers would be prisoners given a chance to work on the settlement in exchange for their freedom. $\endgroup$ May 14, 2022 at 18:58

3 Answers 3


The Dengie Nature reserve


Dengie nature reserve is a 3,105 hectare biological and geological Site of Special Scientific Interest between the estuaries of the Blackwater and Crouch near Bradwell-on-Sea in Essex.[2][3] It is also a National Nature Reserve,[4] a Special Protection Area,[5] a Nature Conservation Review site,[2] a Geological Conservation Review site[6] and a Ramsar site.[7] It is part of the Essex estuaries Special Area of Conservation.[8] An area of 12 hectares is the Bradwell Shell Bank nature reserve, which is managed by the Essex Wildlife Trust.[9]

It consists of large, remote area of tidal mud-flats and salt marshes at the eastern end of the Dengie peninsula . The Chapel of St Peter-on-the-Wall overlooks some of the site.

Nature reserve. Sure it is. Your colony was originally sited here chiefly because of convenient access to London. The morlock-like residents of the colony do not know that they are still on England.


You need a location with a temperate climate and a low indigenous population.

Western or eastern seaboard Canada has potential, but inquisitive Americans are very near. The Americans could easily ascertain what would be occurring there and its precise location. The number of indigenous people could be problematic. They could easily act as spies for whomever. Relocating such large numbers of people would be difficult and problematic.

South Africa has the climate, but too many indigenous people.

Concerning Australia, on the mainland, the most likely locations would be the south west corner, between Perth and Albany; the east coast from Cairns, in the north down to Portland, in western Victoria, in the south. Also, anywhere on the island of Tasmania (during its convict period, it was known as van Diemen's Land). Tasmania is the large valentine shaped island in the south east of Australia. Most of these locations in Australia offer potential to use hydroelectric power, particularly north west and north eastern Tasmania and the mid eastern coast of the mainland. Ignore the rest of Australia, it's too inhospitable.

Most of New Zealand would also be a potential location. If you want easy access to the oceans but some seclusion then the Fjordland region in the south west could be a good location.

The trouble with anywhere in Australia or New Zealand is these would be remote outpost locations far from the main sailing routes, but for British naval activity between India and China, Japan or eastern Russia then maybe they could be useful.

  • 1
    $\begingroup$ Papua New Guinea may be an option. It's not temperate, but neither is Australia, really (im addition to being a desert hellscape full of poisonous animals and nearly Old Testament level insect plagues (I worked on the gasfields there, it's insane). North Western Australia may be an option. $\endgroup$
    – user86462
    May 14, 2022 at 7:40
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    $\begingroup$ @SeanOConnor: Coastal regions of Australia south of 32 deg S generally are temperate, but the rest of the continent, as you state isn't. Regarding PNG, Britain only had the southern half of PNG. The northern part was a German colony. It was only after WWI that Britain acquired the German territories & then later gave them to Australia to administer as a protectorate. A similar thing happened in Africa. Namibia was once known as South West Africa & it was a German territory. After WWI, Britain got it & then gave it to South Africa as a protectorate to administer. $\endgroup$
    – user81881
    May 14, 2022 at 7:52
  • $\begingroup$ I didn't know that about PNG. I always thought Samoa was Germany's only Pacific holding. In Africa, Tanzania was the same too, IIRC. Re: PNG, the mountains probably make the land connection non fatal (but I think British Guiana makes the most sense of all).I know a lot of Australia is temperate in theory, but the giant anticyclone makes it pretty meaningless, apart from near the coasts and Vic / NSW (and of course, Tasmania). $\endgroup$
    – user86462
    May 14, 2022 at 10:01
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    $\begingroup$ +1 for Fiordland, the only problem is the lack of food (even the Maori couldn't survive there). A little further up the West Coast and you come to areas that these days are prime dairying country, and were loaded with coal and gold and timber and fish. Not at all silly. Somewhere around Lake Haupiri might work. $\endgroup$
    – user86462
    May 14, 2022 at 10:07

British Guyana

Britain had one colony in mainland South America. It was a bit of a backwater and in real history, operated by absentee slave owners. Its main exports were bauxite and gold. Just keep out the pesky Venezuelans. The Spanish got kicked out in 1811, so the only developed nation likely to come snooping is the USA, and even that is less likely than in Canada, plus bodies can be easily hidden in the jungle.

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    $\begingroup$ In real life, much of South America remains undeveloped and, in some areas, poorly explored. So, this would be a good location. Not to mention the various accounts of tunnels and subterrain features that explorers and natives have reported. The thick jungle would greatly aid in concealment. $\endgroup$ May 14, 2022 at 19:02
  • $\begingroup$ I'm 90% sure we're on the same page here, but it was/is a real place. $\endgroup$
    – user86462
    May 16, 2022 at 19:10
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    $\begingroup$ Yes I know you are referring to a real colony. I am referring to the fact that large parts of South America remain untamed even to this day, so this colony could serve that purpose very well. Thanks for the info. This may be the most helpful answer yet. $\endgroup$ May 17, 2022 at 3:46
  • $\begingroup$ All's well, we were on the same page :) $\endgroup$
    – user86462
    May 17, 2022 at 6:10

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