Originally posted by Renlish:

FYI, there are mods that allow you to build in all the instance aspects of the game (ie, caves, crypts, etc) if you really want to. It's kinda fun and cool.

Honestly, that would be kinda neat.

Not sure about Burial Chambers, Crypts, or Mountain Caves.. but Troll Caves could certainly be made as makeshift smelting bases at least.

Still hope we get a proper Cave system-type biome at some point. Maybe have to fight Jörmungandr as the biome boss.