One of the last unexplored areas on the Earth, Jewel Cave is more than 127 miles in length (as far as it's been mapped as of yet), making it the third longest cave in the world.

"As little as 10 percent of the cave has actually been seen," National Park Ranger Merrith Baughman informed our group as we started the cave's scenic tour, a moderately strenuous half-mile loop which took us through large caverns and narrow passageways.

"A lot of people want adventure," Baughman said. "There's just something about going down into a different world."

Formation shaped like a strip of bacon, one of the wonders of Jewel Cave

For those interested in a more daring cave experience at Jewel Cave National Monument, there's a three-to-four hour long spelukning tour that lets visitors get down and dirty. Participants must be able to squeeze through a 8 1/2 inch by 24-inch crawlspace at the beginning of the tour. They must be in good shape and must be able to handle heights and small spaces (one length of the cave in this tour is called the "Brain Drain"), but it's guaranteed to be a once-in-a-lifetime experience.

For a different, less hands-on experience, there's the Candlelight Tour. It's still pretty strenous, as participants must carry lanterns and climb steep wooden stairs, but it gives them a chance to step back into the 1930s for almost two hours.

Whatever your taste, there's a tour at Jewel Cave that will suit you.

In summer, reservations are recommended. Call (800) 967-2283 to reserve a place on any of Jewel Cave's tours.

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