1) Cave exploration 
Entering caves or caverns for the purpose of recreation or exploration. Spike (Camp)
speluncing, spelunking; potholing (UK), caving (UK) 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 co...