The sunken structure looks like the victim of a catastrophic flood.

The Church of the Annunciation was carved into the face of a cliff, just like the rest of the town of Haute-Isle.

The post-apocalyptic remnants of a bucolic town ruined by a plane crash.

A French valley with forests so lush it was nicknamed "the Small Amazonia of the Pyrenees."

This ancient Roman bridge and aqueduct still stands as a wonder of classical construction.

A medieval military street hidden beneath a charming French fishing village.

This innocuous-seeming building is actually the remnant of a major wartime brothel.

A natural arch carved by a river gave its name to the so-called "Cave of Forgotten Dreams."

These quaint French houses dangle precariously over a precipice.

The largest underground church in Europe.

Historic medieval fortified city in southwest France.

The mental institution where Van Gogh created some of his most famous work now allows guests to walk in the artist's footsteps.

Noirish green neon marks the location of one of the oldest private detective agencies in France.

An icy lake tucked among jaw-dropping alpine panoramas.

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

High atop the Eiffel Tower is a small apartment built exclusively to entertain the science elite and make the rest of Paris jealous.

This 1,300 year old monastery built atop a single rock was once only accessible depending on the whims of the tide.

Now a memorial to merchant sailors and Titanic victims, this medieval church was destroyed by bombing raids in 1940.

A half-mile-long stretch of medieval forts built after a devastating pirate attack persists amid the modern port city.

A cruise ship retraces the the route of the doomed RMS Titanic, 100 years later.

This 700-year-old storehouse was a POW jail, aviation workshop, and Titanic memorial before becoming a brewpub.