I once had the experience of crawling through underground tunnels and caves. It's called Spelunking.
Crystal clear waters, rugged caves and underwater caverns are just a taste of what Bruce Peninsula National park has to offer.
Peppersauce Cave in southern Arizona is relatively well known but not a tourist attraction. It's in a wilderness area on the north side of Mt. Lemon in the Santa Catalina mountains north of Tucson.