Lechuguilla Cave in Carlsbad Caverns National Park, Guadalupe Mountains, New Mexico, has a 2010 surveyed length of 130 km. It is a hypogene cave, formed by uprising H2S-bearing fluids which oxidize to form sulfuric acid when they reach oxygen-bearing meteoric water. The cave is formed in the Permian Capitan Reef Complex. Argon-argon dating suggests that the cave is on the order of 5 million years old. Lechuguilla Cave exhibits dramatic mineralization, particularly gypsum chandeliers, native sulfur, and many massive calcite speleothems. Of particular interest is the microbiology of the cave where microbes, present and past, formed without surface interactions.