Cave tours allow spelunkers a first-hand view of humankind's earliest homes and Mother Nature's earliest attempts at feng shui. Stroll through nature's architecture with this Groupon.

Choose Between Two Options

• $54 for a four-hour High Adventure cave tour for one (a $109 value)
$99 for a four-hour High Adventure cave tour for two (a $218 value)

Certified vertical cave guides begin the journey in the Siphon Room, where they drain a pool of standing water to clear the way into Riverbend Cave—a winding rock passageway that gives way to vertical drops. Using lead ropes, they instruct climbers in basic rock climbing, allowing them to slowly scale down the smooth rock walls to view Achilles Pit, which houses a four storey-tall crystal formation and ancient toys carved by Santa's elves.

Guides supply guests with all necessary spelunking equipment, though participants should bring cameras, sturdy footwear, and two layers of clothing, as guests may get cold or wet along the journey. Tour participants need no previous climbing experience.