If we do make the world a bowl putting another world on top of it seems kind of... weird? It'd be dividing the world up into two worlds when I really think we need to stick to one.

Also, honestly, we need to figure out a lot of things before we decide if demons are a thing and one would be stuck inside of a smaller planet floating above the other one.

The only reason I suggested the Inverted Black Tower is that it's kind of its own thing.