Fun Caves replaces the default caves with a dense system of mostly flat (and easier to navigate) caverns, with biomes owing much to caverealms. Once you go underground, you should find everything you need to survive without ever returning to the surface.
Note: This mod is not compatible with mapgen V6, and worlds created with the previous version of fun_caves will NOT work with the new one (no matter how many other mods you add in).
Code: LGPL2, textures: CC-BY-SA and CC0
Mod dependencies: default, dye, flowers, vessels
Big Trees (killer bees are not included)
Booty (the chests found in dungeons and pyramids)
Fun Tools (chainsaw, flare gun, rope ladders, wall hammer, etc.)
Huts (primitive villages)
Inspire (rewards similar to the metal/gem crafting requirements)