Find the city of Rapture.
From Create Your Own Story
You swim around in the ocean for awhile, when suddenly you find an entire underwater city! Signs give you knowledge that this place is called 'Rapture'. A bunch of weird 30's ads hang on the walls of the clear glass hallways.
You can see gunfire whizz by in the hallways, between some 30's looking guys and a guy in a diver suit.