GamesRadar: Talk us through the evolution of the setting. Rapture has got to be one of the most unique and complex environments in videogame history. Where did you begin?

HP: We always knew that the game was going to be scary. The horror element precipitates directly from System Shock 2. There's something about Rapture's isolation that makes it really attractive as a haunted house-style game.

But the original vision was this science fiction world - the city under the ocean. So the beginning of Rapture was really functional. If you're going to build a city under the water, you need to keep the water out. You need valves and bulkheads. A lot of the initial design references were nautical, like WWII-era ships and submarines.

But if you were ambitious enough to build an underwater metropolis in the 1940s, you would want to show that off. It's sort of like a skyscraper. You would want there to be gigantic windows looking out into the ocean. So that was a focal point of many rooms - an ocean view with fish swimming by. The architectural motif extends to arches and doors that have fish jumping over them, as well as textures on the walls with stylized waves.

HP (continued): On the other hand, building a city underwater is too ambitious; they just didn't have the engineering technology back then to make it happen. So the sea is actually leaking in, and that was a whole other design concern. We wanted the place to feel wet and humid. We want puddles and water cascading out of ceilings. The place is getting crushed by the pressure and it's going to flood any second now.

I don't know who came up with the idea that Rapture was built in the 1940s, but the time period really fits Andrew Ryan's vision of a world that's engaged in horrible conflict. And if you were going to build a metropolis during the 1940s, it would probably be art deco. And the philosophy of art deco, that we are ascending to the next level, almost transcending our humanity, fits in metaphorically with the idea of Adam, that humans can be better than they are now.