A cave dwelling that was started by the Celts, expanded by monks, and finished by knights.

An icy lake tucked among jaw-dropping alpine panoramas.

This frog-themed restaurant was frequented by Picasso, Saint-Exupéry, and more.

Walk through spectacular aisles of hanging meat and wagon wheel–sized cheese at the world's largest wholesale food market.

Original cabaret handbills, posters, and feline artwork are a purrfect highlight of the Museum of Montmartre.

Statue of death tucked in the University of Medicine courtyard.

Exquisite wall sculptures carved in secret by an early quarryman in an obscure corner of the Paris Catacombs.

A subterranean shelter remains intact under a busy Paris railway station.

Egyptian Revival movie palace abandoned for decades and restored in 2013.

Behind the pink curtain, Au Bonheur du Jour, an art gallery of erotic archives.

"In the Dark" Restaurant in Paris offers dinner in complete darkness.

France's national museum of scientific and industrial instruments.

One of the oldest medical collections in Europe focusing on rare surgical instruments.

This home designed for chocolate magnate Antoni Amatller is an exquisite treasure-box of Catalan Modernism.

An early 20th-century bullring converted into a modern shopping center.

This quaint Spanish village agreed to be painted blue as a marketing stunt but found that they preferred it that way.

Abandoned Nazi train station turned underground astroparticle laboratory.

The former 1920s mansion of a prominent Catalan developer was used as the Soviet Embassy during the Spanish Civil War, and there is still a bunker below the garden.

This massive fiberglass Gulliver turns every visitor into a Lilliputian.

A Franco-era dam flooded (almost) everyone out of this centuries-old Aragonese town.

This amazing example of Valencian Art Nouveau looks more like a cathedral than a public market.

This awesome Spanish castle is so fantastical it was actually used on Game of Thrones.

A once grand hotel now sits eerily abandoned in the Catalan countryside outside Barcelona.

Considered the birthplace of the Copper Age and Bronze Age, the river is tinted red from 5,000 years of mining.