A cave is a natural underground hollow space that is completely dark. The entrance area of caves are home to many creatures such as snakes, mice, spiders & porcupines. Only a few animals are found deep in caves. Bats often live in caves. Another common creature found in caves are cave crickets. Caves consist of narrow passageways (corridors) and chambers (caverns).
Caves are usually formed when underground acidic (sour) water corrodes (=wears away) softer stones, such as limestone, leaving only the hard rock, such as granite, left. They can also be formed during natural catastrophes, such as earthquakes or by ice and glaciers.
People in the past are known to have lived in caves and even today caves can provide shelter for trekkers. Many European caves have been inhabited (=people have lived in) already in the Stone Age, and some caves have beautiful paintings on the walls.
People who explore caves are called cavers (or speleologists). They go into caves for fun, exercise and to see the different formations. This can be a dangerous sport because caves sometimes have deep pits. Cavers also have to climb and crawl through the passages.
Cavers usually go into caves with four or more people. Each person has 2 or 3 light sources. One light is attached to each helmet. People go into caves to try and explore more about the world.
The study of caves is called Speleology.