The sinister ruins of one of the worst dam failures of the 20th century lie in this astonishing alpine setting.

This wondrous waterfall rushing down a green-covered mountain wasn't discovered until 2010.

A quirky bookstore hidden beneath a sea of whitewashed Greek villas.

This observatory within Europe's first dark sky park offers stunning views of the night sky.

An open-air museum in a mountain valley features works designed to blend in with—and disintegrate back into—their natural surroundings.

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

The field of tiny caves that mark this Chinese cliffside are each their own historic Buddhist temple.

Rippling sand dunes frozen in the Arizona rock.

The intricate stonework of Machu Picchu serves as a testament to Incan engineers.

Wondrous sandstone hoodoos where Native Americans collected clay for pottery, 9,000 years ago.

The world's longest known cave system.

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

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

A modern-day wunderkammer dedicated to Indianapolis history, Afrofuturism, and musical vibrations.

A natural gas leak provides a flickering flame beneath a waterfall.

Legacy of the earthquake that nearly wiped Lisbon off the face of the Earth.

Though its celestial ceiling is impressive, the true star is the vast collection of French books.

This ancient village and its adjoining cemetery have a beautiful history of death and remembrance.

An isolated dive site teeming with cnidarians.

A lovely aquatic park built by a one-armed Civil War veteran who made a fortune from lotuses.

A grand Gothic Revival basilica with stained glass depictions of Montreal's religious history has only one soul resting in its crypt.

A labyrinth of ancient tunnels hidden below the city holds the ruins of 2,500 years of history.

Five candy-colored villages on the Italian Riviera.

Sitting on an Italian hilltop is this surreal fortress built by the mad inventor of electrohomeopathy.