Caves are compelling for many reasons. Here are two views: the hobbyist's and the scientist's.
The Sport of Caving
At its core, caving is a wilderness experience like mountaineering or scuba diving. The object is to go somewhere that's hard to get to and see things ordinary people never see. If you're totally immune to claustrophobia and enjoy getting muddy, being in top shape, and partying hard with similar people, then find yourself a circle of cavers and get down with them.
Exploring a cave is an unforgettable experience. Yes, commercial caves with lights and guided tours like Mammoth Cave National Park are plenty memorable, but I'm talking about smaller, wilder caves. There may be some in your neck of the woods that you never heard of unless you're connected to the network of cavers (find some in the Caves list). Earlier in my life, I was, and I squirmed my way through a few of upstate New York's caverns with no commercial potential.
There's a deep thrill connected to entering the Earth and going beyond the bounds of light and safety. You challenge your limbs, lungs and nerves like no other sport. The sights of the underworld, like a row of clean stalactites in a silent chamber flooded with mirror-flat water, rank right up there with moonrises in the woods.
The people in this sport are part of the fun too. Some cavers (only lazy reporters call them spelunkers) specialize in photography or cave diving, others in rescue work. Some crews dig new entrances to known caves. There are even folks into cave radio. But all of them are fiercely devoted to preserving the underground from destruction at the hands of thrill-seekers. And the danger of caving, which can injure or even kill the inattentive, keeps the focus on safety and training. On the whole, cavers are the most clear-eyed, coolheaded romantics you'll ever find. And did I say they're men and women in top physical shape who like to party hard?
The Science of Caves
However, when I went to college and studied geology, not much that I learned had anything to do with caves. In the eyes of the geologist, caves are as temporary as beaches. They're essentially an early stage of erosion in limestone country, openings dissolved by groundwater where it meets the air, at the water table.
Soon enough—in a few thousand years, that is—caves open up to the surface as sinkholes. If the water table is steady for a long time, you can get a peculiar dry terrain called karst that has no surface streams. (The word comes from a district of Slovenia that's riddled with splendid caverns like Postojna.)
Beyond their intrinsic interest to specialists called speleologists, caves are valuable for geologists—for instance, caves have fossils in them, like early human remains. And because they have always been sanctuaries of one kind or another, caves preserve the oldest examples of human art.
When I think of caves now, long after my caving days, I think of things like the underwater rock formation from Devils Hole in southern Nevada. It's a piece of cavestone that preserved in its layers a record of the ancient atmosphere for the last half-million years. It's a scientific treasure, every bit as important to our knowledge of recent climates as the ice cores retrieved from Greenland, Antarctica, and a few places in between. Cavers (or, to be more respectful, speleologists) went into the wilderness and found it for us.
PS: Mines are another kind of underground space. These days, the frontier questions of physics and cosmology call for experiments to be done in deep labs in old mines to detect WIMPs—so-called dark matter particles that are almost totally invisible.
