A Tour of the Planes
Sigil, the City of Doors, is a large metropolis located in the Outlands atop The Spire, the large column of stone at the center of the plane. It has the shape of a torus; the city itself is located on the inner surface of the ring. There is no sky, simply an all-pervasive light that waxes and wanes to create day and night. Sigil cannot be entered or exited save via portals; although this makes it quite safe from any would-be invader, it also makes it a prison of sorts for those not possessing a portal key. Thus, many call Sigil “The Bird Cage” or “The Cage”. Though Sigil is commonly held to be located “at the center of the planes” (where it is positioned atop the infinitely tall Spire), some argue that this is impossible since the planes are infinite in all dimensions, and therefore there can never truly be a center to any of them, let alone all of them; thus, Sigil is of no special importance. Curiously, from the Outlands, one can see Sigil atop the supposedly infinite Spire.
Sigil is ruled by an enigmatic power known as the Lady of Pain. There is much speculation regarding her origin, but nothing is known for sure. She doesn’t concern herself with the day-to-day minutia of the city, only intervening when some sodding berk breaks one of her laws. Those who attract her attention can count themselves lucky if they don’t live to regret it.