Check out this absolutely amazing cave we discovered recently. It started by me finding a small sinkhole in the woods and dropping a rock down it and hearing the rattle and clank of it tumbling down a narrow shaft and rolling into a much larger cavity or tunnel. It took us several days to chip and blast through the rock to make the opening large enough to drop into.
We did, and were both amazed at the very impressive and beautiful speliothems (cave formations) and the knowledge we were the very first people to ever get into that space to explore. Not many of those places left here on Earth and when you find one it is always an exciting and magical discovery!