This tunnel was built in order to protect the village of Daroca from flash floods during rainy seasons.

Rare karst landscape eroded from a flat seabed.

Bacteria and algae give the salty water its bubblegum hue.

Peek into a cave of giant, glimmering crystals.

This seaside sanctuary was once one of the most important religious sites for women in ancient Greece.

This legendary city has been a tourist attraction for centuries.

Controversial site of what could be Europe's first pyramid.

Celebrated example of Ottoman architecture that also served as a site for brutal massacres.

This brutalist monument is inscribed with 9921 names of Yugoslav partisans who perished during WWII.

This unusual piece of Renaissance art depicting the bodily horror of crucifixion and skin disease may have been inspired by fungus-induced hallucinations.

A unique museum tells the story of the day-to-day life of World War I soldiers.

A Parisian boutique devoted to la Sape, the elegant Congolese fashion subculture rooted in European colonization.

A 400-year-old church covered floor to ceiling in ex-voto offerings from the faithful.

The Argonaute submarine was the French navy's pride and joy in the 1950's.

This soviet pilot's graveyard is filled with headstones made of airplane fins.

Abandoned Soviet base once stocked with short and medium range missiles pointed at western Europe.

A modern, secular take on a traditional Virgin Mary motif.

These miniature works of art are hiding in plain sight on buildings around the city.

Stockholm's decidedly unique public transit system has doubled as the world's longest art gallery for decades.

The highest cold-water geyser in the world.

This historic toy museum brings a little whimsy to a city not usually remembered for such things.

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

For a brief time in 1960s France, families could climb into a tiny submarine and be pulled along an underwater journey.

The macabre collection of Jacques Sirgent, an expert scholar on the undead and all of their trappings.