The Outlands

Like the Astral Sea, the Outlands was a plane between the Outer Planes. It was the plane of neutrality, incorporating a little of everything and keeping all aspects in a paradoxical balance—simultaneously concordant and in opposition. The plane had varied terrain, with prairies, mountains, and shallow rivers.
The Outlands was circular, like a great disk. In fact, those who envision the Outer Planes as a wheel once pointed to the Outlands as proof, calling it a microcosm of the planes. That argument might have been circular, since the arrangement of the Outlands inspired the idea of the Great Wheel in the first place.
Around the outside edge of the circle, evenly spaced, were the gate-towns: sixteen settlements, each built around a portal leading to one of the Outer Planes. Each town shared many of the characteristics of the plane where its gate led. Planar emissaries often met in these towns, so it wasn’t unusual to see strange pairings, such as a celestial and a fiend arguing in a tavern while sharing a fine bottle of wine. Of course, that was before the Whispered One's apothesis.

A Plane Torn Asunder

When the lich lord Vecna enacted the Rites of Ascension, he transformed the energy and essence of the Outlands into a magical force that fueled his apothesis. Light, color, and life itself funneled out of the plane and into his being, utterly destroying a once vibrant landscape. Twenty years later, the ruins of the Outlands lie silent, coated in a heavy layer of dust and haunted by shadowy monstrosities that slipped through the now-unguarded dimensional gates.
While Vecna's rites left the Outlands a lifeless shell without a hint of magic in itself, his ritual did not capture the many magical items that passed through the plane in trade caravans and the pockets of adventurers. Daring explorers willing to fight through the monsters that have taken up residence in the ruins may find enchanted items, forgotten artifacts, lost knowledge, and more simply by picking through the rubble—assuming they can make one of the old entry portals function in the first place.

Sigil, City of Doors

At the center of the Outlands, like the axle of a great wheel, is the Spire—a needle-shaped mountain that rises high into the sky. Above this mountain’s narrow peak floats the ring-shaped city of Sigil, its myriad structures built on the ring’s inner rim. Creatures standing on one of Sigil’s streets can see the city curve up over their heads and—most disconcerting of all—the far side of the city directly overhead. Called the City of Doors, this bustling planar metropolis once held countless portals to other planes and worlds.
Sigil was a trader’s paradise. Goods, merchandise, and information came here from across the planes. The city sustained a brisk trade in information about the planes, particularly the command words or items required for the operation of particular portals. Portal keys of all kinds were once bought and sold here.
The city was the domain of the inscrutable Lady of Pain, a being as old as gods and with purposes unknown to even the sages of her city. Indeed, the Lady's power may have been the very reason Vecna chose to drain the Outlands of energy for his ritual. Whatever the case, the Lady of Pain now lies half dead in her chambers, unable to move, her life essence sustained only by an amulet forged from the heart of a titan.

Type

Dimensional plane