Formation

Caves are formed when acidic water from rain erodes softer rocks like limestone, leaving behind harder rocks like granite. 

Size

The world's largest cave is Hang Son Doong, or Mountain River Cave, in Vietnam's Phong Nha-Ke Bang National Park. 

Features

Stalactites and stalagmites are well-known cave formations. Stalactites hang from the ceiling, while stalagmites form on the floor. 

Habitat

Caves provide homes for many animals, including bats and insects. They can also be home to rare, endangered, and threatened species, as well as microbial communities that only exist in those caves. 

Cave art

Cave art is made up of paintings and engravings that date back to the Ice Age, roughly 40,000–14,000 years ago. The first cave painting to be recognized as Paleolithic was Altamira in Spain. 

Discovery

Most caves in the world are undiscovered. If you discover an unmarked cave, you can name it. 

Flooding

Most caves are prone to flooding. 

Sea caves

Sea caves form when waves erode faults and fractures near the water's edge. Over time, the cave can become open at both ends, creating a natural bridge or arch. 

Spelunkers

Scientists who study caves are called spelunkers.