planescape
Planescape is a campaign setting from dungeons and dragons. First made during 1e AD&D, but later more officially published in 1994 for 2e AD&D, it takes place in the planes beyond the material plane, using Sigil--the City of Doors as it's known--as its primary "hub" location.
In 1999, a video game was released by Black Isle Studios based on the setting called planescape:_torment, which allowed play in Sigil, the Outlands, Baator (also known as the Nine Hells), Carceri, and the Negative Energy Plane.