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

Remains of Roman amphitheater hidden in a sleepy quarter of Paris.

This surreal statue brings a famous French novel about a supernatural cad to arresting life.

A modern-day Lascaux cave underneath Paris.

A lone cannonball remains lodged in the walls of the Hotel de Sens as a sober reminder of a revolution.

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

How did a French journalist’s grave become the sexiest statue in the cemetery?

In the best of all possible worlds, everyone will get a chance to see this statue in which Voltaire's heart is interred.

An overlooked marble is the only surviving in-place 18th century example of the measurement that changed how we define distance.

The ruins of a Duke's bucolic dream, where camels once roamed alongside "Dutch" windmills and faux-Italian vineyards.

A majestic lion statue guards this Parisian botanical garden, and feeds on an unsettling item.

Indents in the pavement are all that remain from a grisly death machine in Paris.

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

Stroll through retro Paris while shopping for old postcards and discarded doll heads.

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

France's national museum of scientific and industrial instruments.

This charming cobbled backstreet is the most Instagramable street in Paris, much to the residents' annoyance.

A museum of magic with a Sadist past.

Walk upon the mementos of the dead in this Parisian courtyard paved with medieval tombstones.

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

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

The vast, legendary catacombs hold secrets much stranger than stacked bones.

This sweet-toothed bear searching for snacks has been a symbol of Madrid for decades.

Not far from Madrid, a set of perfectly preserved trenches date back to the Spanish Civil War.