A modern-day Lascaux cave underneath Paris.

The curious underground history of keeping Paris clean.

One of the last realized projects of an influential, self-taught, French Modernist architect Jacques Couëlle.

The largest refracting telescope in Europe is housed on the grounds of a former French castle.

The former global standard for the exact mass of one kilogram sits under lock and key outside Paris.

Ghosts of France's colonial past.

Stripes of human ashes cover a back lawn in the most sought-after burial grounds in Paris.

Ordinary art transforms to extraordinary thanks to locals' quirky sense of humor.

This Georgian mansion blends historical significance with an impressive art collection within picturesque surroundings.

Across from a hotel parking lot, a Confederate spy rests under a large tombstone with her Union Veteran husband behind a copse of trees in a small, well-maintained cemetery.

The tombstone of an unfortunate explorer who disappeared in the Paris Catacombs.

A simple plaque on the facade is the only reminder that the treaty ending the American Revolution was signed inside.

Medieval museum built over Roman baths that features famous tapestries of a lady and a unicorn.

The celebrated eyesore created by starry-eyed sweethearts.

The oldest continuously operating mint in the world that has been making coins since the 9th-century.

The approximate spot where the last Grand Master of the Knights Templar was put to death.

This iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.

A counter-culture bookstore like no other hides in plain sight in the streets of Paris.

This structure atop a craggy cliff in one of the most beautiful parks in Paris boasts an unbeatable view.

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

One of Hollywood's most iconic actresses was born in an upscale Brussels neighborhood in 1929.

At a rest stop north of Seattle, you can drive through the trunk of an ancient tree.

A charming easy-to-miss sculpture garden filled with whimsical and thought-provoking metal sculptures.

Trimmings from the record-setting tree line that surrounds Cirencester Park have been used to manufacture chemotherapy drugs.