Would this LARGE ET Gecko Cave fit, or possibly look weird, in a 20L Zilla Critter Cage 30"L x 12"W x 12"H ?

I have a 38L or 10 Gallon Cage and it fits perfect. In my opinion a 20L cage is too small for this cave.

This may sound stupid, is the bottom of the cave open or is it just that hole?

It’s two pieces, the top and the bottom and when closed it has only that hole for enter/exit. So it’s like a piece that fits perfectly to make it look like a cave.

Would this look wierd in a Zilla cage that is 24x12x12? What about room left over??

I personally don't think so. They love this item. It takes up most of the cage but honestly they love it.

What are the dimensions of the cave. It isn't showing the description.

This is rather roomy for it's appearance. It is approximately 5 inches wide by 3.5 inches deep by 3.5 inches high. I have two large leopard geckos that share it with no problems.