Lechuguilla Cave in New Mexico is the deepest limestone cave in the United States (and the 4th longest). Lechuguilla Cave is one of the most beautiful caves in the World, and is full of speleothems and troglobionts found nowhere else on earth. It is very difficult to visit Lechuguilla because the National Park Service tries to keep it in an undisturbed state. In one instance after the theft of a very famous cave pearl, the cave was closed completely for several years.

Recent scientific discoveries at Lechuguilla Cave hold immense potential for scientific research. But the caves are extremely fractile, as the selenite formations may be destroyed even by slightest changes in humidity. Humans breathing in a huge hall for some time even caused the collapse of fragile gypsum chandeliers.