Adolph Sutro's little-known, geographically inaccurate, deprecated monument.

Unparalleled stargazing, one of Colombia's best observatories, and a swimming pool can all be found in the middle of this ancient tropical forest.

The caldera of this mini-volcano has been turned into a naturally heated mud bath.

A 10 million-ton rock once worshiped by the Tahamies Indians, accessed by an astounding staircase.

Enchanting cave with a river crashing through the roof.

A dangling church built over a Colombian gorge.

This picturesque mansion has gone from opulent ruin to nature museum.

An explosion of natural color known as "the river that ran away from paradise."

This medieval castle overlooking the Elzbach river looks just like it did hundreds of years ago.

Breathtakingly blue walls shimmer inside the "Glacier Behind the Town."

The world's largest model of our planetary system.

The world's first ice hotel is still one of the most elaborate and beautiful.

These azure waters were thought to lead to the Mayan Underworld.

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

A Hawaiian stairway to heaven—that you can't climb.

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

A gargantuan crystal kingdom.

Its buzzing collection honors vibrator history.

Once the most densely populated place in the world, this island is now a ghost town.

Aqueducts have dramatically changed this old lake, now home to tufa towers and its very own species of tiny brine shrimp.

A beautiful geyser under environmental threat.

This shop specializes in oddities and Victorian-inspired wonders.

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

Cabaret where the show girls are all androids, and the patrons couldn't be more pleased.