A spelunker is someone who explores caves as a hobby. It describes people who venture into dark underground passages armed with headlamps, helmets, and a sense of adventure.

Spelunkers squeeze through narrow tunnels, rappel down vertical shafts, and wade through underground streams to see what lies beneath the earth's surface. They might discover magnificent rock formations called stalactites and stalagmites (stalactites hang from the ceiling like icicles, while stalagmites grow up from the floor). Some spelunkers find ancient fossils, underground lakes, or chambers so vast you could fit a cathedral inside.

This hobby requires careful preparation and respect for the cave environment. Spelunkers usually go with a group, let someone know where they're going, and bring backup lights since getting lost in total darkness would be terrifying. They also take care not to damage delicate cave formations that took thousands of years to form.

The term spelunking is used mostly in the United States. In other English-speaking countries, people usually call this activity caving or potholing, and serious practitioners often prefer the term caver to describe themselves. Whether you call it spelunking or caving, it's the same thrilling pursuit: exploring one of Earth's last wild frontiers.