1. The sport of walking and climbing in caves.
2. A sport which involves climbing into and around underground caves.

Caves have been explored out of necessity for thousands of years, but only in the last century or two has the activity become a sport.

In recent decades spelunking has changed considerably because modern-protective wear and equipment have improved the safety factors.

It has recently come to be known as an "extreme sport" by some; although it is not commonly considered as such by its participants.