Sigil

Also known as the Cage, the City of Doors, or, less commonly, the City of Secrets, a floating city centered around the top of an infinitely tall spire in the center of the Outlands and the self-proclaimed center of the Great Wheel.

A major hub for interplanar travel, the city contains multiple portals to every single plane, as well as to numerous locations on the Prime Material Plane.

Sigil has a complicated politics consisting of many scheming, ideologically-opposed factions, but is ruled absolutely by the mysterious being known as the Lady of Pain.