A cave is a hollow place in the ground, specifically a natural underground space large enough for a human to enter. Caves form naturally by the weathering of rock and often extend deep underground. A cavern is a specific type of cave, naturally formed in soluble rock with the ability to grow speleothems. Visiting or exploring cave for recreation may be called caving, potholing, or spelunking. Shelters grottos though strictly speaking cave exogene, meaning deeper opening wide shelter is endogene. Anchialine talus corrasional or erosional fracture speleology layers more soluble minerals, such as gypsum, dissolve out from between layers less stalactite stalagmite dark calcium carbonate precipitation sedimentation. 4K UHD 3840×2160.