Lechuguilla Cave in the context of "Speleothem"

Caves or caverns are natural voids under the surface of the Earth and have been observed in other rocky worlds also (viz. on Mars). Caves often form by the weathering of rock and can extend deep underground. Exogene caves are smaller openings that extend a relatively short distance underground (such as rock shelters). Caves which extend farther underground than the opening is wide are called endogene caves.

Speleology is the science of exploration and study of all aspects of caves and the cave environment. Visiting or exploring caves for recreation may be called caving, potholing, or spelunking.

A solutional cave, solution cave, or karst cave is a cave usually formed in a soluble rock like limestone (Calcium carbonate, with chemical formula CaCO₃). It is the most frequently occurring type of cave. It can also form in other rocks, including chalk, dolomite, marble, salt beds, and gypsum.