I used to work with a bloke who would work for 6 months or so to save enough money to spend the rest of the year caving and potholing. He told me some hairy stories of squeezing through miniscule tunnels and swimming underwater to reach some underground cavern. He absolutely loved it. I don't feel comfortable even in the lit up tourist places; stalagtites and stalagmites remind me of some of HP Lovecrafts freaky creatures, all slimy and tentacled!