I was reading on wikipedia about the Githyanki and their civilization sited upon the Astral Plane. I've never been one for having any real interest in TSR or WOTC's world creation (that's their universe for them to play in - this is mine etc. etc.) but I was taken by the idea of the God-Isles, the immense petrified remains of dead and forgotten gods. These vast relics float throughout the Astral Plane, providing islands of gravity and normal time flows amist the gravity-free, timeless expanse of the Plane.
The floating island idea attracts me - it's very similar to the concept that crops up time and time again in Japanese CRPGs, and also in one of my favourite films, the really rather wonderful and beautiful Laputa - Castle In The Sky. It struck me that a campaign world could be located on one of these islands.
Since travellers in the Astral Plane have silver cords attaching them to their point of origin, the Plane has always been associated with the colour silver to me. Therefore I got thinking that an aboriginal race of Astral Plane humans could live in a city atop one of the floating God-Isles under silver skies. Without a sun, merely an ambient illumination, there would be no day/night cycle.
This contrasts nicely with the idea of dark dungeons under the surface of the "world". We now have an eternal "noon" above ground and an eternal "midnight" below it. This fits neatly in with the idea of the mythic underworld discussed on many of the OD&D blogs recently. Now the tunnels and catacombs are no longer just extensions of the "real" world that happen to be underground but almost another dimension, one with a strong element of metaphor and dream-world to it. I like this.
Another theme I like is that of Howard's Lovecraftian tale "The Black Stone". The denouement of this tale is that a black monolith in Hungary turns out to be a spire of a massive fortress buried under the level of the ground and that the cliffs below it are the grown-over battlements and walls. Such a fantastic idea - the idea that our world, the neatly-contained little world of the tale is actually just a layer on top of and around an older reality is such a great concept that I've always been amazed as to why this tale isn't up there in the pantheon of OD&D must reads alongside with Vance and Poul Anderson. I would have never discovered this tale without reading Harms' Encylcopedia Cthulhiania, an excellent reference work to all things Cthulhu Mythos.
Anyway, I like the idea of a random chunk of debris floating across the Astral Plane striking the surface of our campaign world/island and breaking down into the stone ground exposing the tunnels, pits and workings of the mythic underworld. The PCs entry to the dungeon would be via this sink-hole.
Why are these tunnels, pits and workings inside the dead God? That's an question for another blog-entry but I strongly suspect it will something to dead the nature of the God before it died.