Less than 1 mile east of Volcano, this National Natural Landmark has the whiff of a tourist trap, but one look at the array of helictite crystals – rare clusters that grow horizontally – makes the crowd more sufferable. Guides for the 50-minute tours are experienced cavers. For more eye-catching rock formations, head to the Zen Garden, where a short trail twists through a cluster of Tolkien-esque marble slabs.
Note that there are five flights of stairs on the tour.
