A cave's a natural underground void large enough for a human to enter. Some people suggest that the term cave should only apply to cavities that've some part that doesn't receive daylight; however, in popular usage, the term includes smaller spaces like sea caves, rock shelters, and grottos. Speleology's the science of exploration and study of all aspects of caves and the environment which surrounds the caves. Exploring a cave for recreation or science may be called caving, potholing, or, in C… (More on Cavern)