Not a lot, but the Shasta Caverns are very cool. Guide tours only. Another is the Oregon Caves outside of Grants Pass. However, when we come on old mine shafts, we will explore them. There are two near where my son lives we have been in. They were opened after hydraulic mining washed off the top layers and exposed an ancient creek bed. The whole strata had been turned on its side so the tunnel drops and rises. Fun in the dark. Both tunnels are from the same "mine" but different locations. Whenever we come across mines we will explore them. There are numerous shafts in the Oregon City, CA site, but I don't want to brave the poison oak to get to them. We have been in another in the same general area that goes about 80' down and has a Toyota pickup in the bottom, but we didn't have the industrial size mosquito repellant with us. Someone has to remain up top to operate a winch to lower and raise people on that one.