In my world I want to create a really deep underwater science facility to conduct weird and unethical experiments in. But I think to myself: How deep could I take such a building?

Does it become easier to withstand ocean pressure with a larger building because you can increase the size and strength of structural components? Or does it become harder because its more surface area for the ocean to attempt to crush? Or does size not matter at all and it all depends on how the structure distributes the pressure?

Bonus points if you have suggestions for maximizing the depth of an office building (or larger) sized underwater facility.

  • $\begingroup$ Bigger is generally worse. This is because the shape of the surface gets flatter and less curved as shapes get bigger. $\endgroup$ Commented Mar 5, 2018 at 7:54
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    $\begingroup$ Bigger is generally not more of a problem than just the challenge of making it bigger. You just have to endure the pressure of the water column above you. If the structure is bigger than there is more water column above it, but also more structure to support it. Twice as big should just be twice as expensive but not more difficult. $\endgroup$ Commented Mar 5, 2018 at 8:24
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    $\begingroup$ Don't forget that in addition to the main structure, you will also need a submersible capable of the same depth so you can travel to and from it. And you'll also need a very robust docking interface to allow you to move between the sub and the facility. The docking interface could very well become the major weak point in any structural design. It is certainly possible to make a very large and robust pressure vessel that will survive deep water pressures, but the requirement to be able to get into it and out of it will result in compromises that may be fatal. $\endgroup$
    – Simba
    Commented Mar 5, 2018 at 12:47
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    $\begingroup$ @VilleNiemi Bigger is only a problem if we're assuming open space. An ant colony/hamster tube setup could be upscaled fairly easily, I'd think. $\endgroup$
    – Carduus
    Commented Mar 5, 2018 at 15:09
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    $\begingroup$ I'm only here because I misread the title as "underwear facility" $\endgroup$
    – Quintec
    Commented Mar 5, 2018 at 19:01

5 Answers 5


Your structure would definitely need to be spherical, since that shape supports so much more pressure than hard angles. (The human part of the bathyscaphe which descended to the bottom of the deepest trench in the ocean was the little sphere at the bottom of the picture. The rest was gasoline, water and iron to regulate buoyancy.)

Since we've gone to the very bottom of the ocean, you can thus put your underwater lair as deep as you want to.


To withstand the enormous pressure of 1.25 metric tons per cm² (110 MPa) at the bottom of Challenger Deep, the sphere's walls were 12.7 centimeters (5.0 in) thick (it was over-designed to withstand considerably more than the rated pressure).

There are many practical problems, though, with building and living in such a pressure vessel:

  1. you're going to need a lot of steel,
  2. building it will not be a secret,
  3. towing a monstrous, and monstrously heavy, round office building into the deep ocean will be, to put it mildly, difficult,
  4. you've got to keep the outside painted to prevent corrosion,
  5. all the welds must be perfect (in the deep, water will quickly cut through any crack, rapidly opening it),
  6. it must be powered, warmed, etc,
  7. the crew must be fed,
  8. it must be maintained.

Best just to hand-wave the details.

enter image description here

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    $\begingroup$ On the bright side, if you're operating at Cthulu's depth having a building with no corners is a definite advantage. $\endgroup$
    – Racheet
    Commented Mar 5, 2018 at 11:35
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    $\begingroup$ Another big problem: It's easy to get suplies at your door, but how will you open that door? $\endgroup$
    – Madlozoz
    Commented Mar 5, 2018 at 12:47
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    $\begingroup$ @Madlozoz once the supply sub is securely connected to the lair's (wet) air lock, that water is not under pressure anymore. Just open the lock from the inside, and let the water drain into the desalination plant. $\endgroup$
    – RonJohn
    Commented Mar 5, 2018 at 14:38
  • $\begingroup$ And if you are willing to handwave enough details you can end up with something like Rapture from the Bioshock series. Maybe not in the challenger deep, but you could build on a sea mount or somewhere a little shallower. A scientifically plausible Rapture would be an interesting setting. $\endgroup$
    – AndyD273
    Commented Mar 5, 2018 at 14:43
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    $\begingroup$ Heating and power generation would be much less of a problem if it's situated near a volcanic/thermal vent that could provide both. $\endgroup$
    – Bohemian
    Commented Mar 5, 2018 at 16:23

You can make the structure pressurized to match water pressure. Then you do not need to worry too much about structural integrity, and make it as large as you want.

The cost is multi-hour (de)pressurization required while entering or leaving the facility. This could be a useful security feature as well: to prevent unauthorized access, and unauthorized departures. The movie DeepStar Six (1989) has an example of explosive decompression. Here is an RL example of the setup necessary for an unauthorized diver to reach your deepwater facility.

You can build it in pieces, but single large and round structure will have better volume/wall area ratio.

It will cost a lot, so research should be extremely high-value, and do not plan any large open areas in there. It will be a submarine.

Edit: I did mean to say that underwater structure has air pressure comparable to water pressure outside of it. I believe this can be done as part of Saturation Diving:

the divers live in a pressurized environment, ... [e.g.] an ambient pressure underwater habitat.

I still feel this is overkill for the goals. A better way to hide a secret lab underwater is to get a nuclear-missile submarine, and replace missile silos with labs and extra life support. It cannot go deep, but it can move around, it is designed to stay stealthy, and it can stay underwater for months.

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    $\begingroup$ There's a limit to how much pressure humans can survive. Using a pressurized structure limits you to about 675 meters deep. $\endgroup$
    – Mark
    Commented Mar 5, 2018 at 4:53
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    $\begingroup$ Why will you need (de)pressurization when transiting the station? Your submarine would dock with the lair just like a space capsule docks with the ISS. $\endgroup$
    – RonJohn
    Commented Mar 5, 2018 at 5:06
  • $\begingroup$ @RonJohn Agreed - I suspect the inside of the facility will have to be at atmospheric pressure (even if the outer structure was pressurized), so as long as you then enter from a sub or through a tunnel with over-surface entry, you're good to go. $\endgroup$
    – user46537
    Commented Mar 5, 2018 at 6:50
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    $\begingroup$ "You can make the structure pressurized to match water pressure." - not if you want humans inside you can't (well, you can, but only up to a certain - pretty low, limit). High pressure gasses do nasty things to you - even pretty inert ones like helium. $\endgroup$ Commented Mar 5, 2018 at 13:33
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    $\begingroup$ @MrGerber My reading of the answer is that the suggestion is to not have the inside at atmospheric pressure. $\endgroup$ Commented Mar 5, 2018 at 13:34

Do you actually need it to be very deep underwater? If you just want it to be hard to find, you can place it in remote shallow water (well, not really shallow, but something like 100 meters deep). Somewhere near Greenland, or Antarctica would work, if you want to place it firm on the bottom. It's not like there are millions of scuba divers in these places. It might be better not to complicate the story with unnecessarily fantastical elements. Also take into consideration that you are underwater, so you need an earthquake inactive area if you build on the seabed.


That depends on how much you want to isolate that group of people from the surface population. To hide from the police 5 meters below water is enough. Or, really, 5 meters above is well, too. To sponsor a local police station would bring much better invisibility.

If you want to escape from accident observation, you need about -500m, for to hide from the frequent underwater observations - 500m is about the reach of a man in a hardshell suit, something as https://en.wikipedia.org/wiki/Atmospheric_diving_suit. And under a place heavily used by ships - such place will never be used as a base for a bathystat or bathysphere.

And bathyscaphe can reach everywhere, you should hide in the place that is dangerous for them. But seismical regions are even more dangerous for your construction.

And if somebody really wants to find them - he will catch them at passing resources from the surface, even if you hide them in the mantle of the Earth.

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    $\begingroup$ Given the difficulty of finding MH370, I think deep underwater should be just fine. Also, what is a "skafandar"? The only thing google came up with is "slavic word for space suit", and a space suit would be no use at all in deep water. $\endgroup$ Commented Mar 5, 2018 at 13:44
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    $\begingroup$ @MartinBonner Its like one of those old timey diving suits where air gets pumped from the surface so workers can work under water all day. Basically the same thing as a space suit, which is presumably why they use the same word. $\endgroup$
    – jhbh
    Commented Mar 5, 2018 at 13:53
  • $\begingroup$ @MartinBonner Never believe Google's translator without a check :-). But I am sorry, it was my error, of course, I thought the translation will be the same. AFAIK, for deeper diving the hardshell costume is used. Something as en.wikipedia.org/wiki/Atmospheric_diving_suit. Edited. $\endgroup$
    – Gangnus
    Commented Mar 5, 2018 at 15:01
  • $\begingroup$ @jhbh You are right. More often more wide used language has more universal words, and we can almost count on it. But sometimes that rule is broken. And this is my mistake, of course. $\endgroup$
    – Gangnus
    Commented Mar 5, 2018 at 15:03

The merit of having it underwater is that you don't leave tracks.

However the engineering to supply deep underwater structures would be fairly obvious. There aren't commercial submarine freighters at this point.

A better solution to not be blatantly obvious would be to have a submerged entrance to an underground cavern. Now you only need a supply vessel that can do shallow dives for short durations. Pick your location so you have multiple nearby ports.

However it is far easier to hide something in the middle of a reasonably large city.

Consider a cement plant. No one comments on heavily laden trucks running in and out. So hauling away the spoils of digging would be fine.

Next door you have a warehouse facility. Again, 50, 100 semi loads a day is no big deal.

Now you have 10 acres of floor space 500 feet underground. No one can hear the screams.

  • $\begingroup$ As much as people have brought up the difficulty of hiding and supplying such a thing, the remoteness of it is exactly why I want to have it that way. The questions itself was more out of curiosity but what I love is the idea of a place so remote and out of reach that not even the sun can reach it and if anything goes wrong with the system the people inside are left to rot in the the heavy darkness of having thousands of tons of water waiting to crush you from every direction. In space nobody can hear you scream. But no one can hear you 10,000 ft underwater either. $\endgroup$ Commented Mar 6, 2018 at 19:47
  • $\begingroup$ See Frank Herbert's novel "Under Pressure $\endgroup$ Commented Mar 7, 2018 at 22:43
  • $\begingroup$ Ooh I love Frank Herbert! Thanks for the reccomendation, I'll check it out. $\endgroup$ Commented Mar 7, 2018 at 22:51

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