The Secret Caves of America’s National Parks

Beneath the plains of South Dakota’s Wind Cave National Park are 143 miles of underground passages, highlighted by a unique honeycomb formation known as boxwork.

Wind Cave National Park alone holds 95 percent of the world's known boxwork, and nowhere else in the world is the boxwork so perfectly formed. You can explore these formations and the rest of the cave through a variety of tours ranging from leisurely walks through big open passageways to tight crawls through smaller spaces.

Deep underground in South Central Kentucky you’ll find a true natural wonder called Mammoth Cave National Park. With more than 400 miles of mapped passages (only 12 of which are open to the public), it’s the largest cave system in the world. It’s also home to some great cave names, like Frozen Niagara and Fat Man's Misery.

The colorful history of Mammoth Cave begins millions of years ago when underground rivers cut passageways through the sandstone, creating the stunning passageways and formations you can walk through today.

But the history of the park doesn't stop there. There are fascinating stories involving Native Americans (who harvested gypsum from the caves) and slaves (who gave the first tours to visitors 200 years ago), so there’s more than to learn about than geology. The park also offers 85 miles of aboveground hiking.

The aptly named Crystal Cave is just one of 250 known caves in Sequoia National Park, but it’s possibly the most beautiful. While most caves are formed from limestone, Crystal Cave is made of marble that shines brightly when light is reflected through it. You can book tickets in advance at the cave’s website.

The Chihuahua Desert sits today on the site of what was once a tropical desert, and below that desert lies Carlsbad Caverns. Discovered in 1898 by a teenager named Jim White (who went on to be an early promoter and park ranger for the caverns), this underground cave system exists on the spot of a former U-shaped reef.

It is approximately 400 miles long, and more than 119 caves have been discovered within its boundaries. When you visit the park you can explore many of the caves that were discovered and named by Jim White himself, such as the Big Room, New Mexico Room, and Kings Palace; or you can tour the Slaughter Canyon Cave or the bottomless pit (which is actually 140 feet deep).

If you want to really crawl back through the past, try the lantern tour.

No trip to Great Basin National Park would be complete without a tour of the Lehman Caves. This lone multi-chambered cavern is a living cave, still dripping and growing formations at the speed of one inch per year. But what makes this cave most interesting is how long people have been using it—human activity dates back almost 10,000 years to the Paleoindians.