Visit this playground of waterfalls, caves and sinkholes.

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

This rugged area of red rocks and arches is often considered one of the most beautiful places on Earth.

Tour the world's largest deep-hole dimension granite quarry, where you can view the plant where gravestones are made and roll a ball down the outdoor granite bowling alley.

A stone arch leads to a cavernous 1930s spring house tucked away in the Pennsylvania woods.

These banned cigarette vending machines now sell little pieces of pocket-sized art.

This lake in the Cascades lives up to its name, disappearing down a hole every spring.

Read between the lines of the subway map to find the hidden abandoned Civil War fort.

Carved by a waterfall in a hard-to-reach rock formation, this heart-shaped rock has inspired romantics for decades.

This unauthorized stone mermaid was secretly carved out of public stone before being permanently preserved.

Enormous piles of historically significant stones, dumped by Congress in a forest, and abandoned for 60 years.

The oldest surviving synagogue in New York City is now a soaring art space.

The intriguing personal collection of a professional demon-chaser.

Dyed by iron oxide over centuries, these sandstone rocks rise thousands of feet into the sky.

In the middle of an extremely unforgiving and desolate high desert is the most secret military facility in the world.

When ecosystems collide in the arid Southwest.

A morbid secret lies hidden within the beautiful walls of the Boston Athenaeum.

A 300-yard long natural tunnel runs through a ridge deep in the Appalachian Mountains.

Less a museum than a bizarre fantasy world created by artists and engineers.

This free, take-a-book shop seems like a trick but isn't.

The superstar of Cold War nuclear bunkers has been featured in countless films but is now barely operational.

The highest bridge in America was built for an almost unnervingly small amount of money.

A celebration of capitalism in Midtown.

An essential stop before plundering, BYO Cutlass.