Spelunking was the act of exploring a cave.
Travis Mayweather had an interest in rock climbing and spelunking. His experience with these activities helped assist Tucker and Reed in rescuing Denobulan geologists from the caverns beneath Xantoras. (ENT: "The Breach")
Jason Vigo was spelunking in caves on Camor V when he was beamed on board the USS Enterprise-D in 2370. Vigo noticed he was aboard a Federation starship and asked Captain Jean-Luc Picard to beam him back into the cave. (TNG: "Bloodlines")