As of lately I've been taking a look at the old 2e World Builder's Guide. Coming up with a world for an upcoming campaign, I'd like to take an interesting take on just about everything including the world itself. What are some interesting concepts for planets, rather than just being terrestial spheres? I could take the Norse route and have a world tree with different levels. I could take another route and have the world be the remains of a deity. Or I could have the world be a disc on the back of four elephants carried through space on a giant turtle........What are some other interesting options for a fantasy/sci-fi planet?