Caves Humanity has been fascinated by caves since prehistoric times.
Caves provide natural shelter from wind, rain, and predators.
They also engender a sense of mystery, a gateway into subterranean kingdoms populated by strange beasts and supernatural beings. They offer explorers the excitement of discovery and physical challenge, and they offer scientists a unique vantage point from which to study the Earth. The largest and most commonly visited caves are in limestone, the product of decomposition by natural acids and of slow abrasion by particles carried in underground streams. Groundwater in most cave systems picks up carbon dioxide from the atmosphere or soil air, where it accumulates as a by-product of organic decay. Natural fractures in the rock widen, eventually creating a network of open cavities through which water flows freely.