The planar movements and conjunctions described at the beginning of the book work fine within the Great Wheel cosmology. They should be applied to every plane - for example, the Outlands are usually in conjuction with the first layer of the Abyss, but periodically either come into true conjunction or severance. The planar cycles of the Outlands are described
on the Mimir.
Worlds on the Material Plane may only be connected to a few specific outer planes or planar realms. Eberron is a good example of this.
Underland might be a world on the Material Plane; it might be, for example, Oerth's moon of Luna, which has an extensive Underdark.
The Ethereal Sea is simply the Ethereal Plane.
Celestial River is a planar path similar to the Styx, Oceanus, or Yggdrasil, but separate from those. Mostly it flows through the Outer Planes.
Avidarel is a solar system on the Material Plane.
Carigmoor is built on a ruined Material Planar world. See above for my ideas on connecting it to the mercane, Union, and Sigil.
Curnorost is a hidden realm somewhere in the Outer Planes. As above, I suggest either Pelion in Arborea, Niflheim in Hades, Belieren in Elysium, or (as a devastating secret) Chronias in Celestia. It could be in the Outlands, too, in the hinterlands beyond the gate-towns.
Deleur I'd make an unusual realm within the Quasielemental Plane of Mineral, perhaps created by a mineral race like the tsnng before being driven away by an alliance of celestials.
Dendri is a moon on the Material Plane.
Faraenyl is an artificial demiplane created in the Ethereal Plane. As above, I suggest it was made by refugees from the world of Logicus.
Kin-Li'in is a layer of the Abyss. I numbered it the 473rd.
The Lizard Kingdoms are a world on the Material Plane, quite possibly the source of the saurials known to the Forgotten Realms.
The Maze is a demiplane built in the Ethereal Plane using the raw material of the dreams of the imprisoned angel Sophiel.
The Mountains of the Five Winds are a Material world in serious contention by the forces of Limbo and Mechanus.
Ouno is a world on the Material Plane, a crystal sphere half filled with a living ocean.
Palpatur is a world in another part of the Material Plane, devastated by a Blood War incursion.
I'd classify the Sleeping God's Soul as a demiplane, though it could also work as a Material Planar world or even an Outer Planar realm.
I wrote the essay on the Ten Courts of Hell, above, a long time ago and I've since reconsidered. There should definitely be a portal to the First Hell Court in the
Palace of Judgment in the Outlands, but I think they're different enough that they can be considered separate places. I'd put the First Court in Avernus instead; the Second Court could be in another part of the same layer, though my suggestion of putting it in Acheron makes sense given the marauding achererai. The Third Court might go in yet another part of Avernus or even in Malbolge. The Fourth Court, as I said, would be an excellent school to exist in metropolitan Dis; General Yao could teach rakshasas and baatezu alike. The Fifth Court feels like Phlegethos, the Sixth Court feels like Minauros or the Abyss (the Clockwork Serpent Queen could be another aspect of Mammon, actually); the Seventh Court is Maladomini (and the Bronze Bell King could be an aspect of Baalzebul); the Eight Court is Cania (probably an independent realm far from Mephistar); the Ninth Court is an independent realm in Nessus, and the Tenth and Eleventh Courts are so mysterious that there's no grounds for placing them anywhere in particular. The Tenth Court could be a deeper part of Nessus, while the Eleventh Court might be in Elysium or Celestia.
Tevaeral is a world on the Material Plane, and probably the origin of the Order of the Book from the
Epic Level Handbook.
Venomheart is on an otherwise uninhabited world on the Material Plane. The "frequented ports" Daxis and the Obsidian Fens are Material Planar worlds, but Ungaral is a city in Pandemonium and Whitetongue is part of the Elemental Plane of Fire.
The Violet is an ancient, naturally-occuring demiplane.
Yragon is another Material world.
The "looking glass worlds" are usually alternate Material Planes, although the idea of alternate Outer Planes is an intriguing one - perhaps the Outlands has another face, like the other side of a coin, leading to an alternate set of Outer Planes.
