Worlds

Ideas 1
Worlds are giant floating rock platforms. They can be the size of a house, or as large as over 100 megameters (60000+ miles) across and 20 megameters (12000+ miles) deep.

Alternatively, there is one world about 20 megameters deep and anywhere up to or over 2 gigameters across.

The top of a world has its surface. Sometimes there are oceans and continents, or maybe it's just a small park in space, or maybe barren rock. The oceans may flow past the mountain barrier over the edge. I have no clue what happens then. Below the surface are caverns and underground worlds where more creatures live. Under the world there may be reverse rivers where the ocean water goes back into the world somehow, but that can't work with everything can it? Anyway, bat-like creatures may live under the worlds.

Maybe the worlds are actually giant platforms? They could have their supports go down to an underworld. This underworld could be the bottom of space... Or maybe it's a weird dimensional twist, so the worlds are arranged like they were on the surface of a sphere even though they're in flat space. Then, if this were a sphere, inside could be a white hole-like thing, where the universe's energy comes from.

If I ended up going for the floating idea, what's at the bottom of the universe? What's at the top? What's at the edges?

Maybe there's an underworld with Gravitonium? But that seems stupid. And why don't the stars fall? And what is the underworld, where would it end? Is it the planet?

Ideas 2
This just came to me.

I have two ideas for how a world's solar functions would work.

one
The first is that the sun (which is generally either a sentient being, or controlled by one or more such beings) circles the world. It rises over the east mountains/glaciers/ocean (whatever the edge of the world is, and how much water is should allow to escape it) and flies its chariot over the continents and ocean. It then sets in the west and makes its way through the underworld (either a cave system or literally under the world). The issue is how long it would take to cross a large world and how short a time it would take to cross a small one. Even though all the worlds are different, the length of a day should be similar on the earth-like ones. The flatness of the world also causes issues with the light levels - it would be noon pretty quickly after sunrise near the edges. Also, the north and south parts would get little sun. This fits well with them being frozen, but it still seems odd since they'd be REALLY far off from the sun.

two
The second is a variation of the above, where the sun rises through holes in the surface of the world instead of setting over the side and going through holes there. This seems like a better idea, but still strange.

three
The third is that the surface of the world is concave, and the sun rises through a hole in the center of this world. The areas around the center are tropical, and the edges are frozen. The downside to this is that there is nowhere where the sun would ever be overhead. Even worse, the horizon. Since the ground gets higher as you move away, the horizon would bowl up everywhere, and there would be less visible ground than sky (weird sky, since the sun was never in it). Also, oceans might flow towards the center instead of the edges. If this happened, where does the water at the edge come from? Does the water pour into the sun hole, and where does it go from there? What's inside that hole (this applies to the other ideas as well)?