The world's longest known cave system.

Stalactites and stalagmites in a beautifully lit cave.

An ethereal glowing blue ocean cave in Croatia.

This secluded aqua waterfall in the Grand Canyon is the perfect swimming hole, and the Havasupai tribe's fiercely protected natural wonder.

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.

These remote Florida islands have a history of sea turtles and sunken treasures, and one of the world's largest coastal brick fortresses.

The deepest lake in the United States, and once the site of epic destruction that lives on in legends.

The ancient dwellings of the Puebloans, located in the cliffs of majestic mesas.

A beautiful geyser under environmental threat.

In this historic region, homes and churches are carved into ancient volcanic rock formations.

Ruins of a German Castle on top of a towering stone pillar.

Monasteries on rock pillars, once accessible only by frayed ropes.

A seemingly endless landscape of pure salt stretches far across Bolivia.

Thousands of exquisitely carved stone water storage wells, hundreds of stone steps fill this exquisite medieval stepwell.

A layered tribute to the work of mosaicist Isaiah Zagar.

America's most famous piece of self-built architecture.

A psychedelic labyrinth on the San Francisco bay.

Famously misunderstood wonder of the ancient world

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

This faux-seedy Japanese arcade is made up to look like a maze of alleys straight out of a cyberpunk dystopia.

A swing to dangle you off the very edge.

This 1,300 year old monastery built atop a single rock was once only accessible depending on the whims of the tide.

An enormous, inside-out glass globe built in 1935.

A trash dump made beautiful by nature's power.