Crystal clear waters, rugged caves and underwater caverns are just a taste of what Bruce Peninsula National park has to offer.
This is very different from walking through a spacious cavern. It literally involves crawling on hands and knees through underground tunnels. I once had this experience and I'll describe it. It's called Spelunking.
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.