The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

Eons ago, a rushing lava river formed this pristine passage through solid rock.

Behind this beachfront shop lies a spectacular, colorful sea cave with an equally colorful past.

A regular looking rock with an unbelievable history.

It should come as no surprise that the best view of the Hollywood sign is from Batman's lair.

What was to be the world's most secure Cold War document vault ended up as just a few shallow caves.

Towering basalt columns, a creation of fire and ice.

A popular tourist cave with a dark past.

The longest continuous lava tube in Oregon.

A walk through the historic city center, under the streets of Seattle.

Trails through lava-carved tube-caves display sparkling bacteria and a rich history.

Commonly referred to as the most photographed Victorian home in the United States.

No one knows how this Pacific Northwest spruce tree came to have so many trunks.

Climb right into the heart of this colorful Iceland volcano.

This prehistoric sinkhole lured exclusively male mammoths to their death, much to the delight of science.

Enchanting cave with a river crashing through the roof.

A complex of six forts embedded in the Rajasthan hills.

What was once the largest mine in North America has left behind a hollow hill filled with bright blue waters.

This collection of lakeside pagodas and temples are flanked by giant lions, tigers, and dragons as well as their welcoming maws.

Stroll through a wonderland of stupendous moss-covered trees.

This long, dark tunnel is open to hikers, but those without lights are known to get confused even on the straight path.

One of Canada's most incredible rare book collections holds hundreds of thousands of gorgeous tomes that the general public can touch.