13) Lechuguilla Cave, United States
Known as the deepest cave in all of the United States, Lechuguilla Cave is the seventh longest cave in the world as of 2013. It features an entrance size of 90 feet that leads to dead-end passages of approximately 400 feet. It boasts more features aside from its size: this winding and twisting cave is a maze that still has parts to be explored. Huge amounts of sulfur deposits and gypsum welcome cavers who wish to explore it. Different types of speleothems are found here, and some are even unique to this site alone. Rusticles, subaqueous helictites, gypsum hairs and beards, gypsum chandeliers are only a few of the rarely-formed structures. Photo credit.