It's your typical spelunking saga: You squirm through tunnels no wider than a watermelon in diameter, then rappel over the edge of a 200-foot cliff into a void so black you can't even see your feet, let alone the bottom-assuming there is a bottom. If you survive that ordeal, you'll still have to negotiate the slippery slope of the "Freakout Traverse" or the dreaded crevasse known as the "Great White Rift." A subterranean tour through Lechuguilla Cave in New Mexico might also include other highlights and lowlights: "Misery Hole," "Death Pit," and the "Parallel Universe."

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