Lechuguilla Cave is, as of February 2012, with 134.6 miles (216.6 km) the seventh-longest explored cave in the world and the deepest in the continental United States (1,604 feet or 489 meters), but it is most famous for its unusual geology, rare formations, and pristine condition.

The cave is named for Agave lechuguilla, a species of plant found near its entrance. Lechuguilla is in Carlsbad Caverns National Park, New Mexico. Access to the cave is limited to approved scientific researchers, survey and exploration teams, and National Park Service management-related trips.

Lechuguilla Cave was known until 1986 as a small, insignificant historic site in the park's back country. Small amounts of bat guano were mined from the entrance passages for a year under a mining claim filed in 1914. The historic cave contained a 90-foot (27 m) entrance pit known as Misery Hole, which led to 400 feet (122 m) of dry dead-end passages.

The cave was visited infrequently after mining activities ceased. However, in the 1950s, cavers heard wind roaring up from the rubble-choked cave floor. Although there was no obvious route, people concluded that cave passages lay below the rubble. A group of Colorado cavers gained permission from the National Park Service and began digging in 1984. The breakthrough, into large walking passages, occurred on May 26, 1986.

Since 1986, explorers have mapped over 130 miles (210 km) of passages and have pushed the depth of the cave to 1,604 feet (489 m), ranking Lechuguilla as the 7th-longest cave in the world (4th-longest in the United States) and the deepest limestone cave in the country. Cavers, drawn by the caves' pristine condition and rare beauty, come from around the world to explore and map its passages and geology.

In May 2012 a team led by Derek Bristol of Colorado climbed over 410 feet (120 m) into a dome and discovered several new, unexplored passages, pits and large rooms. This new section was named "Oz" and many of its features were named after items from The Wizard of Oz. The discovery included a large room measuring 600 feet (180 m) long, up to 150 feet (46 m) wide and up to 150 feet (46 m) high. It was named "Munchkinland". A pit, named "Kansas Twister", at over 510 feet (160 m) from floor to ceiling, is the deepest pit yet discovered in the park. The ten person exploration team included members from Colorado, South Dakota, New Mexico, California and Arizona. The team spent eight days mapping Oz, adding the largest distance to the survey since 1989, and bringing the total length to 134.6 miles (216.6 km).