Explore underground caverns, but beware what other creatures lurk in the dark. Bring some lights... and some guns
Mods introducing new content into the game.
New ways to deal with enemies, be it attack or defense.
Changes to enemies or entirely new enemies to deal with.
Map generation and terrain modification.
New Ores and resources as well as machines.
Things related to oil and other fluids.
Furnaces, assembling machines, production chains.
Changes to power production and distribution.
I don't think Industrial Alchemy and Subterranio get along.
