The Concordant Domain of the Outlands is the center of the Great Wheel of Outer Planes. It connects to all other Outer Planes and is the only one with truly neutral alignment. Some characteristics of this plane were ascribed to the World Tree cosmology unaligned planes of Cynosure and the Fugue Plane. Both of them survived the Spellplague to float in the Astral Sea.
The Outlands was the exception to many of the rules governing the Outer Planes, the first being its lack of alignment or true neutrality. It was an infinite plane, yet it had a definite center (the Spire with Sigil on top). The properties of all the other Outer Planes were mixed together in the Outlands. Good, Evil, Law, and Chaos existed here in all their forms, but they were less able to affect each other due to the neutralizing effect of this plane. It also defied description by changing the perception of those who entered, becoming a completely new and yet familiar plane with each visit. Deities could not fully control what visitors saw and heard in their realms, but they could influence the appearance to represent their proclivities and portfolios.
Sigil, also known as the Cage or the City of Doors, is the 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. In the World Axis cosmology, Sigil is considered a demiplane.
“Ah, the Cage. Nexus of the planes. You’ve gotta hate it…”
For your campaign
A portal is a large, intangible and invisible two-dimensional circle, but not limited to this in size and shape. Due to this, a freestanding archway of some kind is usually built to identify the location of a portal, so those who could not detect magical auras did not stumble into them accidentally. It is impossible to visually find out a portal’s destination. Unlike that popular wisdom says, sticking one’s head into that field to find out the destination is not possible, as merely touching the portal activates it.
One way to find out the location of a portal is to cast the reliable detect magic. The magical aura of a functional portal is strong enough to be detected with this spell. But finding out more about a portal requires a more complex spell.
New spell: Analyze Portal
Seeing with a magic eye, you sense a portal. Studying it, knowledge about it comes into your mind as though it was a memory you could not recall until now. This spell can be cast by any member of a class with access to identify.
Casting Time: 1 minute
Range: 60 ft.
Components: V, S, M (a crystal lens and a small mirror)
Duration: Concentration, up to 10 minutes
When casting this spell, you can tell how many magic portals are there in range, as well as their specific sizae, shape and location. Once you find a portal, you can study it for one round. If there were more than one, you can only study one at a time. Each round you study a portal, you can discover one property of the portal, in this order:
- Any key or command word needed to activate the portal.
- Any special circumstances governing the portal’s use (such as specific times when it can be activated).
- Whether the portal is one-way or two-way.
- Any unusual property that hasn’t been hidden by a 4th-level spell or higher.
- Finally, a glimpse of the area where the portal leads and knowledge about what plane that location is in.
At higher levels. When you cast this spell using a slot of 4th level or higher, it provides information about unusual properties even if these have been hidden with a spell of the same level as the slot used.
Portals are a fantasy staple, and they were heavily used in the Forgotten Realms campaign setting until the Spellplage changed the cosmology configuration for good. Since there hasn’t been so far an official adaptation to Planescape for 5e, we can just hopefully wait they will still be an importat part of Sigil.