This Florida sinkhole hides a rainforest-like micro-environment in its depths.

The stones of this Incan wall complex fit together so well you couldn't fit a piece of paper between some of them.

Mother Nature outdoes herself with this stunningly beautiful set of caves carved into marble.

The ghost town left by the worst nuclear disaster of all time is being taken over by nature and urban explorers.

This Peruvian canyon is filled with geometric salt pools that have been being harvested since the Incan empire.

Huge stone depressions which may have acted as an Incan agricultural experiment.

A valley of unique erosion patterns lends to a view like nothing on Earth.

Conifers from the Jurassic Period transformed into stone in Patagonia.

This scalding hot river was thought to be a myth until one geoscientist made it his quest to study the mystical waters.

A bright little alley in La Boca is a part of tango history.

Xul Solar was an artist of alternate worlds, inventor of languages, and dreamer of utopias.

Museum housed in underground tunnels that date back to Buenos Aires's earliest settlements.

This historic, palatial theater is now one of the world’s most beautiful bookstores.

A gateway to a mysterious network of underground tunnels.

A fantastical group of cliffside stairways, bridges, and twisting paths carved out of stone provide a surreal coastal hike.

Mineral springs believed to hold therapeutic properties draw in visitors from all over.

Live out your childhood construction fantasies in this one-of-a-kind gyrating hotel.

The nerve center of a massive, state-of-the art radio telescope that sprawls across Western Europe.

An amusement park on the grounds of an unused nuclear power plant, with a swing ride inside the cooling tower.

This miniature take on the Kremlin is one Dutch man's retirement project.

Peek through a transparent pyramid and drink in the mountain made of books.

A historic observatory now an astronomy museum beautifully situated at the moat of the Middle Age city centre.

The platform atop this verdant volcano was built with the help of a royal elephant.

This historic hydroelectric power plant in Japan has been preserved and is open to the public.