Siren's Grotto is a forgotten destination on Rapture's main Bathosphere line. Before the fall of the art deco city, one stop on the line had become unreachable. Some allowed their imagination to define the place in an ironic mirror of what Rapture would become, while others merely thought of it as an unfinished port that was lost, overshadowed by Ryan's 'ambition'.
The 'forgotten' port had been designed as a resort location, set to open with the release of the 1960's bathysphere models, which were meant to connect the public with more easily accessible bathysphere transportation. Unfortunately, Rapture's economy took a dive and the port's construction appeared to come to a standstill. With that, access became limited.