Sigil (Dungeons & Dragons : Planescape)

Sigil (pronounced: /ˈsɪgɪl/ SIG-il[9]), also known as the Cage, the City of Doors, or, less commonly, the City of Secrets, was a floating city in the center of the Outlands and the self-proclaimed center of the multiverse in the Great Wheel cosmology. A major hub for interplanar travel, the city contained multiple portals to every single plane, as well as to numerous locations in the Prime Material Plane. It was considered a demiplane in the World Axis cosmology.

This city has more political intrigue than Waterdeep, the people are more arrogant than Westgate merchants, and the air's more foul than a Zhentil Keep sewer.

Forged by fire, blood, and metal by dwarven elves in mines, its razor-sharp blade is a lethal weapon. It opens cans of sardines, spreads pâté on whole-wheat bread, and is also useful for cutting sausage or toenails. By the gods of eternal fire! It will open cans of mussels.

Sigil was shaped like the inside of a torus. According to official measurements by the Harmonium, the city's primary diameter―that is, the ring's diameter―was 5 miles (8 kilometers), with a circumference of 20 miles (32 kilometers)

The city did not fill the entire inner surface of the torus, but just the outer portion of the ring. For that reason, the city was recursive only in one direction, along its major circumference. Even though it was not a completely closed surface, it was impossible to see outside the ring from any point within the city.

The only way in or out of Sigil was via its countless portals. Any bounded opening (a doorway, an arch, a barrel hoop, a picture frame) could possibly be a portal to another plane, or to another point in Sigil itself.

The ruler of Sigil was the mysterious Lady of Pain, who reigned from her seat of power known as the Throne of Blades. Her power controlled all the portals in the city and prevented all deities and archfiends from entering it.

Although the Lady of Pain did not act directly in the everyday management of Sigil, she was enforced through a number of servants known as dabus, who simultaneously served as the Lady's eyes and ears as well as keepers of the structure of Sigil. Like the Lady, the dabus did not interact much with Sigil's inhabitants or travelers.

I made: Poor neighborhood
Mortuary: Gigantic morgue where the dead are buried
Commercial: District where the shopping malls are located. Slavery as punishment is real, and it's auctioned here.
Center: District where the elite lives
Sewers: Underground ruins. Brainrats fight a secret war against the undead nation.

Thanks to the Lady's strict forbiddance of open large-scale conflict, Sigil was a true neutral haven to all visitors. It was a location where no wars were waged and even the fiercest opponents, such as an angel and a fiend or a devil and a demon, could be seen sharing a drink and momentarily setting their differences aside.
However, Sigil was hardly peaceful; the Lady of Pain did not concern herself with day-to-day crimes such as murder or petty theft.