One of hiking’s subtypes is underground – literally. Caving. It’s exactly as the name implies. Hiking in caves. Like mountaineering or canyoning, caving (or spelunking) can involve a variety of hiking and climbing technique, and depending on where you are caving, it might even involve a bit of swimming or kayaking too. It’s an outdoor sport with a truly indoor mentality.

In caves, you will get chances to see wildlife and mineral formations you may never get to see on the surface of the earth – bats, spiders, worms, and even fish. And to the educated eye, a journey underground is an exploration of earth’s diverse and often violent past. Underground you can see millions of years into earth’s history, with fossils, sediment lines, and formations that have taken millions of years to arrive where they are now.

You should never go caving alone. Some cave systems have hundreds of miles of complexity, and if you get lost, there may be little or no chance of survival. Light is your best friend underground, and without a guide, and especially without light, one wrong step could mean a hundred-foot plummet.

Some caves are more well-explored than others, and there are usually guided tours through some of the more popular caves in the world. A lot of American caves, for example, have already been explored and you can see their tour advertisements listed on billboards for tourist attractions along most of America’s cross-country highways. Though, despite the casual appeal, there is a serious pursuit behind the practice, and new ways to challenge yourself as a hiker, climber, and caver.

If you’re caving, having a good light source and cave-map are extremely helpful. Cave systems are like earth’s capillaries, and are just as three-dimensional. If you’re not sure where something goes, don’t go there. It’s a simple rule to follow as you plummet into the bowels of the earth.