I clicked on the thread thinking I would see a laundry list of "what in the national enquirer" level of stories...
Gotta start somewhere.
Just before Thanksgiving we stayed at Alabaster Caverns in NW OK and there was a decent sized sinkhole about 40' from our campsite. After going through the cave tour we found out that the main cave goes almost directly under the RV sites about 50-60'. so yeah, that was pretty interesting. The fence they had put up around the sinkhole was of the dog pen variety, but they had a special sign placed nearby that gave a history of the types of sinkholes and dangers. Just made it part of the attraction!
Also at the entrance of the cave, the rock wall had collapsed in a recent rain and blocked the whole entry. The tours were given by starting at the exit and turning back around about 3/4 of the way through.
FYI, alabaster is a pretty soft rock.
Surely I can think of some more interesting sights we've come across...