Landmark, at least. Caves are a relatively new and unfinished feature to the game, and in a new video, the developers attempt to explain what makes them an exciting part of the exploration process.
Landmark's caves are layered on top of each other, with each cave system corresponding to the surface biome. Right now, players can delve into only the first tier of caves, but in the future they'll be able to go as far as three tiers down in the search for treasure and crafting mats.
You can watch the full developer video after the jump!