system
Given the following post, respond as if you're commenting on Reddit:
human
[Bioshock] How was Rapture kept a secret?
gpt
Rapture employed a system of fog emitting shrouds to keep people from finding the lighthouse which served as its entrance. Of course, during the initial startup phase, there were problems: mass dieoffs of fisheries, oil slicks, and the like. However, as Rapture's defensive systems (torpedoes, mines, inferred anti-air capabilities) resulted in disappearances of shipping and aircraft that remained unexplained to the wider world - coupled with the extremely inhospitable nature of the frigid North Atlantic meant that a large swatch of sea was left quite avoided: cursed to the superstitious and commercially dead to the rational.

As it was never a particularly well travelled region of ocean in the first place, nobody really felt the loss for this and, by design, Andrew Ryan's shining utopia achieved perfect isolation from the outside world... barring the errant daredevil diver or a domestic situation that would make Jerry Springer gasp. Otherwise, Rapture marches on.