19th century pendulum and a clock restored by a rogue group of guerilla artists.

What if all public housing projects had been designed by "the Pygmalion of modern architecture," not only their prototype?

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

A resort destroyed by a mysterious bombing offers visitors only its remains and the riddle behind it's demise.

Longest canal tunnel in the world, abandoned in the 1960s.

The historic Masonic Lodge in which the first-ever female Mason was initiated.

This banal Parisian entranceway is not what it seems.

An architectural oddity of six stories, accessed by graceful ramps.

This narrow path was cut right into a French mountainside to feed the country's early naval expansion.

The spiral staircase hidden inside this giant Parisian column was likely built for Catherine de Medici's astrologer.

One of the oldest masonic museums in Paris.

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

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

Museum in a swimming pool where the water still flows.

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

135 bronze medallions mark a French meridian line which once rivaled the hotshot Greenwich timeline.

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

This historic island prison holds one of the dungeons from the Count of Monte Cristo even though it is a work of fiction.

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.

The famous winding walk at Chartres is surrounded in mystery and myth.

The largest underground church in Europe.

This statue was given to France by the United States to commemorate the centennial of the French Revolution.

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

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