Caving
Serious and experienced spelunkers can apply to the National Park Service for a special-use permit to explore and map the caves on a volunteer basis. For the rest of us, Jewel Cave offers three main tours with varying levels of comfort and challenge. The scenic tour ($8 adults, $4 children) takes small groups of visitors on a half-mile walk through some of the widest caverns, following a boardwalk with a railing and electric lighting. It’s a great introduction to the intricate boxwork and jagged cavern crystals that make the cave so otherworldly.

For the more adventurous (and the fit), the three- to four-hour wild caving tour heads off of the boardwalk and through some of Jewel Cave’s narrow chimneys and tight passageways ($27, adults only). Participants need to bring their own leather boots, gloves, and knee and elbow pads, as well as demonstrate their flexibility by squeezing into a tight concrete crawlspace above ground. Those who pass the test can don helmets and explore winding, wriggly grottos over three quarters of a mile, glimpsing fantastic and fragile formations like hydromagnesite balloons, thin mineral layers inflated by gas. Wild cave tours are offered in the summer and on selected dates in the off-season. Reservations can be made with the National Park Service.

Somewhere in between is the historic lantern tour ($8 adults, $4 children), a moderately strenuous half-mile route along an unpaved trail, with only handheld lanterns to light the way. There’s no crawling required on this one, and visitors pass through spectacular chambers with names like the Dungeon Room and the Heavenly Room. Lantern tours are offered only in summer.

Hiking
Most of the action at Jewel Cave is underground, but a few trails wind through the forested Black Hills landscape up top. The Hells Canyon Trail is a fun and mildly strenuous 5.5-mile loop through burnt Ponderosa pine forest. In 2000, the 80,000-acre Jasper Fire raged through the Black Hills, burning across 90 percent of Jewel Cave National Monument. The rollercoaster trail hugs a few cliff faces and, along the way, offers an interesting glimpse at the role of fire regimes in a regenerating forest. Mountain bikers are also welcome on the Hells Canyon Trail, a somewhat technical route thanks to downed, charred trees and plenty of rocks.