Karst Regions of the World
...and their caves
Atlas of the Great Caves of the World by Paul Courbon, Claude Chabert, Peter Bosted, Karen Lindsley.
Cumberland Caverns by Larry E. Matthews
Limestones and Caves of Wales by Trevor P. Ford (Editor)
The Wilderness Underground - Caves of the Ozark Plateau by H. Dwight Weaver, Richard L. Walk (Photographer), James N. Huckins (Photographer)
Borneo - Giant Caves of Borneo by Meredith