Barbara Hurd begins her foray into the increasingly popular pursuit of caving as we all would -- with a panic attack. Nevertheless, as her hunger to understand caves and caving increases, she lures the reader in deeper as well, to the extraordinary fascination of these dark spaces. Hurd illuminates the natural history and spiritual territory of caves as powerfully as Kathleen Norris portrayed the Dakotas and Barry Lopez the Arctic. She ranges from sacred caves in India to secret caves in Arizona and, with passionately informed prose, makes these places -- with their stalactites and blind cavefish and ancient galleries of white flowstone and soda straws -- come alive. Characters weave in and out of her story as well: a childhood friend dying of cancer, a wildlife biologist who specializes in bat guano, an elderly Indian guide, and the disembodied voice of a fellow caver, never seen, with whom she spends a profoundly illuminating half-hour. Entering the Stone is both a rich and a compelling natural history of some of the most extraordinary places on earth, as well as a stunning investigation of dark interiors, both terrestrial and human.