cave

A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word cave can refer to smaller openings such as sea caves, rock shelters, and grottos, and they are called endogene caves. Caves which are deeper than its opening is wide are called exogene.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. [URL=https://en.wikipedia.org/wiki?curid=5778]View More On Wikipedia.org[/URL]