The City of Doors is a strange place, a self-contained city-plane. It may be the remains of a strange and ancient god, or the result of a failed planar experiment. Regardless of its origin, it is a singularly curious place.

Few travelers reach the streets of Sigil, which sprawl across the entire “inside” of a toroid plane. Looking into the “sky” of this place, one can see other neighborhoods through the luminous haze.

Travelers can only enter or leave Sigil through portals. It is not a valid destination for more transient means of travel, like a planeshift spell or spell-like ability. Only permanent planar apertures can establish a connection to the City of Doors (including Axis Mundi access points). As a result it is nearly free of genies, drifters, and other planar wanderers. Deities of any power level (anything with a Divine Rank) cannot enter the city, though they can send their servitors.

The City of Doors sees far fewer visitors than any other planar destination. Most first-time arrivals come in the company of residents, and leave the same way.

It is rumored that this strange city-plane is not quite a proper part of the known universe, but part of something else, a fragment or reflection of another place.