Bat Caves, including the Dark Knight.
Bears' Caves, the home of cave bears.
Blue Grottos, sometimes green...
Caves Used as Road Tunnels, or sometimes railway tunnels.
Cave Trekking Tours aka wild caving with a guide, where you can do a little caving yourself.
Cave Visits By Tram.
Cliff Dwellings of the U.S. West
Dragon Caves. Or do you not believe in Dragons?
Gypsum Caves and Mines, all sites related to gypsum.
Gateways to Hell
Living Isolated Underground
Caves with Paintings, which are open to the public.
The Subterranean World Heritage List, a subset of the UNESCO WHL.
Caves With a View, have a look!
World War I