Caves hold a special appeal not appreciated by those who have never been underground. One aspect that I find exhilarating is being in a completely different and alien environment. It smells different, musty and earthy.
Sounds are strangely muffled and close yet bounce around and reverberate in the enclosed spaces.
You're even dressed differently - usually tough, loose coveralls, knee pads, sometimes gloves, sturdy climbing shoes and a hardhat with lamp. You're carrying supplies, emergency equipment, ropes, climbing gear. The plant and animal life are almost surreal - bats, weird translucent slime molds, hairy tree roots, albino amphibians with huge eyes and visible internal organs, furry patches of fungus. And forget the straight lines and comfortable Euclidean plane easiness of moving around on the surface. Half the time you're using hands as well as feet, and you might have to throw in a shoulder, elbow, knee, or your butt for support and leverage.