Rapture, an underwater dystopian city. Secretly built in 1946 on the mid-Atlantic seabed, Rapture was entirely self-sufficient and powered by submarine volcanoes. Constructed by business magnate Andrew Ryan, Rapture was envisioned as the solution to what he saw as increasingly oppressive political and religious authority and populated by those Ryan believed exemplified the best in humanity; as revealed in an audio log, Ryan wanted to create an "Eden", a concept furthered by the resources ADAM and EVE, which are named after the biblical inhabitants of Eden. During the early 1950s, Rapture's population peaked at several thousand, though an elite emerged, discomforting many of the inhabitants.
The development of "ADAM", stem cells created from a species of sea slug, by Dr. Bridgette Tennenbaum, further upset the social balance. ADAM's prevalence greatly accelerated genetic engineering research, creating a plasmid industry that sold everything from a cure for male pattern baldness to skills like telekinesis, with non-passive types like the latter requiring a serum, "EVE." In order to improve ADAM yields, Rapture scientists created the "Little Sisters", young girls with the slug embedded in their bodies. Although initially just ADAM "factories", during the war which later broke out they were repurposed via mental conditioning to extract ADAM from the dead and process it within themselves. At the same time the scientists created "Big Daddies", armed and highly-enhanced humans in diving suits, to defend the Little Sisters as they worked.
For several years, Rapture was what Ryan originally intended it to be: a paradise of freedom and wealth. But ultimately, the very reason it was createdâ€”Ryan's paranoia about world authoritiesâ€”caused the city's downfall, and the ideals Ryan had envisaged to be corrupted and lost. To keep Rapture a secret Ryan forbade outside contact, and, as a result, a black market in smuggled goods sprang up. This market came to be dominated by former mobster Frank Fontaine, who, unlike Ryan, wanted control over Rapture as well as money. His wealth, combined with his monopoly on Tennenbaum's research, soon gained Fontaine enough power and followers to challenge Ryan for control of the city. In late 1958, Ryan lost patience with the conflict, and apparently had Fontaine killedâ€”an action that proved useless, as another figure, Atlas, took Fontaine's place as the leader of the opposition. On New Year's Eve that year, Atlas and his ADAM-augmented followers fomented a riot involving the lower and upper classes. This sparked a civil war between Ryan and Atlas that eventually spread to all of Rapture, crippling the city. As the war progressed, Ryan began to betray his ideals. The former advocate of reason and self-determination began using torture and mind control in his battle with Atlas. Eventually, he became so unreasonable that a number of his supporters attempted to assassinate him. By the time the player enters Rapture, only the "Splicers," citizens with severe mental and physical problems caused by excessive ADAM use, are left, scavenging throughout the city. The remaining non-mutated humans have managed to barricade themselves in the few remaining undamaged areas.
It was not impossible to build Rapture at the bottom of the sea. It was impossible to build it anywhere else.