Sigil is the bustling crossroads of the universe, full of portals leading to every known corner of the planes. It’s called the City of Doors, thanks to the portals that connect it to the rest of the universe, like the hub of an enormous web of relationships and connections.
Sigil is a plane unto itself, existing outside the ordered structure of the rest of the universe and yet intricately connected to it through its unnumbered planar portals. It’s a filthy, noisy city with smoke-choked alleyways and crowded streets. The city is built on the inside of a gigantic, hollow ring that has no outside. To its citizens, though, it’s the center of the uni- verse—vibrantly alive, full of every imaginable treasure.
(Manual of the Planes, pg 25)
Sigil is divided into six regions called wards:
Lower Ward, The Lady’s Ward, Market Ward, Guildhall Ward, Clerk’s Ward & the Hive.
The city is protected by a mysterious entity known only as the Lady of Pain. It is said that her presence prevents deities, demon princes and other aberrant creatures from entering the city.