Well there are references to people just we don't talk to them
Maybe we all are insane and the city was created as a place to put crazy super being so they can't hurt any one and any other people are figments if our imagination and wow that's dark
Thats why you put the supers on another planet and let them take care of stuff their. That is also why there are no super powered beings on earth anymore
Maybe the city is all a part of Abaddon's dark realm created as punishment for the heroes and villains. They strive, die, and revive every day simply for his pleasure.
That thing about opposite Abaddon just sparked an idea for the multiverse thing....
Once we get around to that, how about having him be the big bad? He'd have probably brought the dark realm upon a heck of a lot of places in order to "cleanse the filth", so everything would basically be the RPs version kf Silent Hill's Otherworld.