A cave or cavern is a natural underground space large enough for a human to enter. The term applies to natural cavities some part of which is in total darkness. The word cave also refers to smaller spaces like rock shelters, sea caves, and grottos.
Speleology is the science of exploration and study of all aspects of caves and the environment which surrounds the caves.
World's five longest surveyed caves.
For more, see List of longest caves.
World's Biggest Cave
10 Awesome Caves Of the World
7 Most Amazing Caves of our World
Top 10 Most Amazing Caves of our World
Top 6 Most Amazing Caves
World's Cave Amazing Photos