View from a cave, looking out. This cave is in France

Cave in New Mexico

Cave of Acsibi, Argentina

A cave is a natural underground hollow space. They can have narrow passageways (corridors) and chambers (caverns). They are usually formed when underground acidic (sour) water wears away softer stones, such as limestone. Only the hard rock, such as granite, is left. Caves can also be formed during natural catastrophes, such as earthquakes, or by ice and glaciers.

Caves can have formations in them such as stalagmites and stalactites. These are made over thousands of years by water dripping and leaving mineral deposits.