I would like a world with a big LOT of subterranean space to explore, colonize, and trap ancient evil beings.
Now, while the questions about food and ventilation are well adressed on Worldbuilding, I would like to ask the question geologically speaking.
From what I understand, caves on Earth can be :
- Limestone cave
- Lava Cave
- Artificial caves (quarry...)
The first one exists with system up to 200 km large. The second seems more anecdotic. The tird one doesn't concern us.
What I'm asking for :
What types of cave could we encounter in a World like this, what conditions would create them, and what geologic impossibilities could I encounter ?
What I thought of :
More limestone, More ancient world, allowing more time for nature to carve these caves, More Volcanic activity, More Rain
How can a world with somewhat similar surface to the Earth's one develop these very large underground formations ?
Edited : I did send a sketch at first, sorry.