Sigil

Sigil, also frequently known as the Cage or the City of Doors, is a city-state and the supposed center of the multiverse which includes the Prime Material Plane and all other known planes according to some forms of the Great Wheel cosmology.
People coming to Sigil from the Prime Material Plane are often treated as clueless inferiors by the planar elitists who dwell there. They are thus widely referred to as "the Clueless", "berks" or more charitably, as "Primes". It is highly recommended that planewalkers new to Sigil employ a guide, known locally as a "tout," lest they be taken advantage of or mugged. Such guides can be little better themselves, though, either serving to persuade a traveler to the side of their faction or simply robbing their "customer" once their back is turned.
==Geography==
Sigil located inside of the Outlands, a plane at equal distance from each of the Outer Planes, hovering above an immensely tall landmark known as the Spire that sits at the plane's center. In a certain fashion, this puts Sigil at the center of the planes, at least according to the Great Wheel cosmology, but since the multiverse is infinite in all dimensions there is no true center. Still, Sigil is the closest thing to a center (other than the Prime Material Plane) that there is.
Curiously, from the Outlands one can see Sigil atop the supposedly infinite Spire.
Sigil has the shape of a torus and the city is located along the inner surface of the ring. It is generally agreed by knowledgeable people that this should be impossible, since the center of the Outlands is void of any and all magic, and yet it apparently is. Theories to explain Sigil's location and existence vary wildly, though one of the more popular is that the Lady of Pain either created it or keeps it intact — or both.
There is no sky, simply an all-pervasive light that waxes and wanes to create day and night. The city 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, giving Sigil its nickname "the Bird Cage" (or simply "the Cage").
Sigil contains innumerable 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. Thus, the city is a paradox: it touches all planes at once, yet ultimately belongs to none; from these characteristics it draws its other name: "the City of Doors." This feature make Sigil a prime destination for travelers as well as a center of trade throughout the multiverse.
===Wards of Sigil===
Sigil is divided into six districts, called wards, listed below:
*The Clerk's Ward, an affluent district, home to most of the city's lower-rung bureaucrats and middlemen.
*The Hive Ward, the slum and the ghetto, home to the poor, the rogues, and the unwanted dregs of the city.
*The Lady's Ward, the richest and most exclusive section of the city, is home to the elites of society and of its government.
*The Lower Ward, an industrial district, clogged up with the smoke from the foundries and from the portals to the Lower Planes.
*The Market and Guildhall Wards are the home to the traders, craftsmen, artisans, guild members and other members of the middle class.
==Government==
The ruler of Sigil is the mysterious Lady of Pain. The Lady is sometimes seen in Sigil as a floating, robed lady with a face bearing a mantle of blades. The Lady does not concern herself with ruling the city directly; she typically only interferes when something threatens the stability of Sigil itself or crosses one of her few but unforgiving edicts, which amount to keeping the peace and refraining from worship of her. The Lady is an entity of inscrutable motives and often those who cross her path, even accidentally, are flayed to death or teleported to her hidden "mazes", extra-dimensional labyrinths, and lost forever. It is widely believed that she never speaks, although some unconfirmed rumors to the contrary do exist.
Although the Lady of Pain does not take action directly, she does act through a number of servants known as dabus, who simultaneously serve as the Lady's eyes and ears as well as maintaining the structure of Sigil. Like the Lady, the dabus do not interact with Sigil's inhabitants or travelers much and it is best to leave them be, since antagonizing them can bring down the infrequent but harsh wrath of their mistress.
Sigil is, theoretically, neutral ground to all: no wars are waged there and no armies pass through. Furthermore, no power can enter into Sigil; the Lady has barred them from the Cage. Of course, Sigil is hardly peaceful; with such a condensed population, consisting of everything from angelic devas to demonic glabrezu, violence is common, usually befalling the foolhardy, the incautious, or the poor. Most natives of Sigil ("Cagers") are quite jaded as a result of living there.
Sigil is also home to several extraplanar "factions," which struggle with one another for power and prestige but generally do not engage in open conflict. The Lady of Pain tolerates the existence of these factions so long as they do not interfere with her or her nebulous goals and several even serve useful purposes, such as the Guvners, Harmonium, and the Mercykillers, which serve as the judges, jury, and executioners of Sigil, respectively.