#19 Batman: Arkham City
Arkham City is the world of Batman writ large. It is what happens when you take the seedier portion of Gotham City and turn it into a gigantic prison by building a fence around the imaginary borders.
Even so, it's huge—and Arkham City is made even bigger thanks to the inclusion of the underground city that lies beneath the stones of Gotham. Did you know that there used to be a city where Gotham now stands? Well, I didn't either—at least not until I played the game.
You can either fly around the city on your gliderrific batwings or treat the city as your playground in Catwoman's chapters. It's a wonder how she manages to run around so much without tiring herself out.