My War of the Wolves campaign world has a working title, Cathule. I have my reasons. Mouthfeel is important.
Cathule is a jewel adrift in the endless night of the stars; you can look at all the other living worlds, but not touch them.
However, winding roads conjoin these worlds together into constellations, ever-shifting.
Think of it like a subway map: there are your Fey Crossings, connecting through many places along a green line, but also the Path of Fire, connecting volcanoes to the City of Brass. Where many have died, a dark road will spring, while the gates of Luth and Abrys spring into the cysts of the earth. These between-places are not necessarily sharply divided either from the real-places they connect or from each other; where there are train stations there are different businesses than where there are not, and services spring up to match the character of the line.
So there isn’t exactly a world of the dead, just paths of the dead, leading… somewhere else, somewhere more deadwards. The paths are heavily trodden, and the crossing points have more in common with each other than the world in which they are set. When you sleep, you wander green paths; sometimes in circles, sometimes arriving somewhere. Since the gates of horn and of bone are traveled so frequently by mortals, those paths are easy to access. However, they’re extremely organic; the genius loci of those places dictates a lot about them.
The best paths are the bullet trains of heaven, the well-worn Astral Portals; well known, directed, predictable, discrete corridors which bend space and time. Their converse are Abyssal Rifts, holes in the world, which are extraordinarily dangerous and usually lead (ultimately) to Abyssal hellscapes.
Cathule is a very large domain (although not the largest). That’s its charm, and why it seems to be so central: it’s huge and well connected; fey and shadow realms cluster just out of sight everywhere, and even more distant realms can often be reached by those who know the ways: This burial mound, that stone circle; midnight on such a date, dawn for such a person.
I’ll talk about some of these near neighbors soon.