For those interested in learning about DEEP caves and the people who explore their depths, the book Blind Descent by James M. Tabor is excellent.
For those interested, check out "Blind Descent": http://www.amazon.com/Blind-Descent-Quest-Discover-Deepest/dp/1400067677/ref=sr_1_1?ie=UTF8&qid=1323522109&sr=8-1
Very cool! I just finished reading Blind Descent by James Tabor, and I highly recommend it.