Series of underground houses inhabited continuously for centuries.

This crumbling, graffiti-covered mansion sits tantalizingly within reach of the proletariat who frequent a public park.

These crumbling Nazi artillery bunkers are now fair game for massive graffiti projects.

If they push on just the right spot, even the weakest person can move this titanic boulder.

A centuries-old complex of hand-dug stone chambers has sheltered locals in times of trouble.

This ancient theater was once the home of fierce gladiatorial battles.

The world's tallest bridge is also possibly the most elegant.

There has been an astronomical clock on this spot since the 14th century.

Ivy-covered Medieval tunnels cut through this charming town in France's Loire Valley.

Sleep in a climate-controlled plastic bubble for the night.

The narrowest street in Paris.

Beggars were miraculously "cured" of their fake ailments when they returned home to this 17th century Paris slum each night.

A mosaic-tiled house built by graveyard sweeper Raymond Isidore.

This stunning French estate was so lavish that it landed its original owner in jail for the rest of his life.

Lyon, France is home to two remarkably preserved Roman theaters, one dating back to 15 BCE.

The only remaining collection of flayed figures made by French "madman" Honoré Fragonard.

Avant garde house of Pierre Cardin on the Cote d’Azur.

Hundreds of hidden passageways weave through the old quarters of Lyon.

At Monet's beloved home you can still see the Japanese bridge, waterlilies, and weeping willows that were the subjects of some of his most iconic paintings.

Ancient paintings known as the "Sistine Chapel of Cave Art."

A grotto-like lodge decorated with gilded mosaics, rocks and a noisy waterfall was the setting for the most sumptuous pleasure house of 1900s Europe.

The subterranean "lake" below the Paris opera house inspired the Phantom of the Opera's lair.

A favorite Paris bar for U.S. expats, including Gershwin, Hemingway, and James Bond.

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