Originally posted by JoePasta:

Hey, not sure to the extent and will try more today but i was able to build a fire place in a mountain cave two days ago. it was in a low flat area that looked like it could be used to build in. I only had materials for a fire place as i had fallen into a under ground lake inside this cave. i wanted to dry off so i built a fireplace. i think i could of build other stuff but not sure honestly. the firepit went up no problem though and dried me out with rest points.

I built a fire and a wood grill in there and called it Camping Cave on my map. :D But workbenches can't be put down (from my very limited tests in crypts and caves), so anything that doesn't need one might work.