First, let me make this statement. I have never put on a hat with a headlamp on it and wiggled around through tight spaces underground hoping against hope that I don't get permanently lost. This same fear of getting permanently lost is what compels me to keep a street map close at hand at all times when visiting an unfamiliar city. I have, however, clad in jeans, tee shirt and a light jacket taken several cave tours.
On one such tour, my partner and I were guided through a cavern located on a private farm in Wisconsin. Our guide was a member of the family which owned the land. She was in her mid teens and almost, but not quite, unbearably perky. In one of the underground rooms local teenagers over the years had written or carved their names into the rock walls. She pointed out her grandfather's signature, which dated from the 1950's. She also showed us stalagmites and stalactites and taught me an easy way to keep the two terms straight. "Stalagmites grow from the floor, stalactites hold tight to the ceiling." Mineral laden water dripping through the rock and soil above the caves create these fantastic underground structures. This same process created a massive block of black onyx worth thousands that was too heavy and too deeply embedded in the cavern floor to be moved.
In other caves we have experienced blind albino fish and amphibians inhabiting underground streams and, by dipping our hands into the dark waters, felt the icy chill of an underground lake.