What if the planet is just a big dirt clod clogging up a wormhole, and so the "underworld" is just another outer surface somewhere else in space
Originally Posted by Tvtyrant
Hmm, maybe the spin of the planet pins everything except the core itself to the inner "surface" of the planet. The core acts like a sun that is permanently stuck at noon, rotating in place as a hot dull lump of iron. Water vapor and clouds are turned into steam and blown back to the "surface" as hot vapor so it's very lush and tropical without a lot of standing water. Like a green house space colony.