Fire under high pressure is more efficient and less stable. Splicers camp around burning barrels, oil slicks are everywhere, the player launches rockets and deadly incinerate plasmids into just about everything. Rapture, especially when the player arrives in Bioshock, is also a city that appears to be continuously on fire. Oxygen becomes toxic and nitrogen induces a drug-like state, appropriately dubbed by early divers “ the rapture of the deep”. This comes with its own problems, because gases and human physiology behave very differently at increased pressure. Rapture is leaky, so an equalized environment would go a long way towards making the city stable. If the pressure within Rapture were equal to that of the sea outside, then the force pressing in on the buildings would be equalized. You could get around the problem of pressure by increasing the air pressure with Rapture. A Rapture in disarray would quickly become a very chilly place. Water is a great thermal conductor, so residents of a deep-sea metropolis would need a continuous, massive source of heat to stay warm.

Once you get past the surface, the sea rapidly cools to about 4☌. Deep-sea divers and submersible occupants need to layer up to keep warm. Maintaining even a small underwater structure is hard. Jacques Cousteau’s Conshelfcould operate at depths of 100 meters, while the US Navy Sealab worked at almost 70 meters, but most others were only ever launched in 10 to 20 meters of water. There have been numerous underwater habitats built for human occupation over the years.

Sphere is the operative word here, because a sphere is equally strong in all direction, in stark contrast to the art-deco buildings that make up Rapture’s sea line. Even vehicles like Alvin, Shinkai, and Jiaolong have pressure spheres up to 3 inches thick.

Vehicles capable of carrying humans to the deepest ocean (and there have only ever been 2: the Trieste II and the Deepsea Challenger) have pressure spheres with steel walls 2.5 inches thick. This is the major limiting factor for all deep-sea exploration. For every 9.8 meters you descend the weight of sea water above you increases by 1 ATM (the total weight of all the air pressing down on you at sea level). The first, and most obvious, is pressure. There are several factors that limit how deep you could build a city like Rapture. We also get a glimpse of coordinates near the end of the game (63° 2°N, 29° 55°W) which would place Rapture a few hundred miles west of Iceland (though those coordinates may not correspond to the actual location of the city, but the location where the main character hijacks a plane).

This is evident through the name of the train system in Bioshock 2–Atlantic Express as well as from the literary inspiration for the city–in Atlas Shrugged, Galt is said to have glimpsed a shimmering city beneath the sea while sailing across the Atlantic. We know a few general things about Rapture.

Bioshock rapture book