Not a rave read, but it is an engaging analysis of the personalities of people who participate in extreme caving. The two principal subjects are Bill Stone, who explored vast Cheve Cave of southern Mexico, and Alexander Klimchouk who oversaw the exploration of the supercave Krubera of the Republic of Georgia. Both are scientists with a drive to discover the deepest cave on earth, in addition to advancing scientific exploration. These speleology teams must be in top physical and mental condition to endure the dangers inherent in this pursuit. Their efforts are basically analogous to mountain climbing in reverse, except in some ways more dangerous because of the lack of natural light and the possibility of being buried. There's also a lot of water underground that at times must be plunged through to get to an opening within a cave. At this time, the Krubera cave is the deepest known cave in the world, very steep and plunging, but the Cheve Cave is the deepest in the Americas. The Cheve cave also seems to contain more cavernous areas that can actually hold a few Boeings! The book also delves into the science and history of speleology, covering earlier expeditions to find the deepest caves. All in all, the author does a good job of providing the reader with an armchair experience of caving; one feels the depth, danger, and the triumph that accompany such expeditions. Don't miss NPR's story about this book on All Things Considered - there's also a stunning image of the cavernous Cheve cave in Mexico.