Sigil , or The City of Doors, was a plane of existence at the center of the multiverse, that Adira Harper fled to during the year 1716/1717. It was notable for its strange shape: that of a torus. The gravity curved along with its shape, allowing one to walk along its inner tube without being pulled backward. To the stationary observer, it would appear that one would be walking up the wall.
Sigil was notoriously difficult to get to, despite being known for its many portals to and from it. This was because each of its portals required a specific "key" which could be any object. Unsanctioned portals were illegal, and frowned upon by the ruler of Sigil, a woman known only as "The Lady of Pain". Nevertheless, creating a portal to sneak into this place was possible, as Ellie Wick was able to do it, but she was a powerful and high-level tinkerer, and thus, exceptional in this regard. Most people couldn't do it.
Sigil was broken up into several different Wards. One of these Wards was The Hive, and it was the dirtiest, sketchiest part of Sigil. This was where Adira was said to be hiding, in a tavern called The Bronze Toad.
Queen Aludra Wyrmsbane, Jaela, Ray, Ellie Wick, Eckhart Dayhammer, and Ros traveled here (using a portal machine created by Ellie) in an attempt to find Adira Harper, who was in hiding there. They encountered a Githyanki brigand, who attacked them, only to turn and flee, and be killed when his back was turned. They were able to find The Bronze Toad with the help of a devious "Tout" (a kind of specific guide). Inside, they found Adira, who sent Dayhammer into a Maze, and promised to reveal everything.