A cavern is a large chamber within a cave, a subterranean hollow— some with astonishing dimensions. The word cavernous implies a place where body and psyche can be lost, a sanctuary where philosophical speculation, à la Plato, can blossom. The words cavern and chamber are sometimes used interchangeably with cave, but the cave is labyrinthine, a maze of subterranean chambers, galleries, and passageways, while the cavern is the biggest room of them all. Mark Twain described the discovery of such a space in The Adventures of Tom Sawyer: “Tom went ﬁrst, cutting rude steps in the clay hill as he descended. Huck followed. Four avenues opened out of the cavern which the great rock stood in.” Carlsbad Caverns National Park contains more than 100 limestone caves, outstanding in the profusion, diversity, and beauty of their formations. The details of caverns—dripstone features such as stalactites and drapery—are fragile environments affected by human activities and natural processes both above and below ground.