Superman isn't welcome here.
Gotham is a northeastern American port city of several million in the DC Universe. It is the home of Batman and the majority of his Rogues Gallery.
The opposite of Metropolis, Gotham is far more gritty, corrupt, and filled with a more common criminal element, but still boasts a robust population and decent shopping district. Much like Metropolis, Gotham is basically a stand-in for New York City—Metropolis is often considered New York during the day, while Gotham is New York at night. The Christopher Nolan films, however, based Gotham much more on Chicago. Gotham and Metropolis, incidentally, also happen to both be long-standing nicknames for NYC.
It is a good holiday destination for agents who enjoy the atmosphere of Ankh-Morpork's crime-riddled Shades, but are inclined to a more modern canon, enjoy edible food, or are simply tired of being mistaken for Guild Assassins.