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

The oldest giants in Catalonia are now displayed in a 14th-century Gothic church.

Gaze upon chocolate sculptures depicting everything from chariot races to Gaudí's famous church at this shrine to sweets.

A beautiful but toxic fountain of mercury.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

Week-long block party becomes a competition for the best decorated street.

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

The floorboard scrawling of a tragic madman is on public display outside a Paris hospital, much to the dismay of its opponents.

Abandoned railway line circling the city of Paris.

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

The headless bodies of more than 1,300 guillotined victims of the Reign of Terror are buried here in mass graves.

Natural history museum celebrating biodiversity with a parade of taxidermy animals.

A haunting collection of the vanished and disappearing natural world.

The history of radiation is on safe display at the foot of a radiation science laboratory.

A scandalous Art Nouveau collaboration that set Paris all atwitter at the turn of the century.

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

A popular shrine where the Blessed Virgin allegedly appeared in 1830, displaying a holy armchair and two incorruptible remains of Lady Saints.

The remaining relics of the patroness of Paris lie in a chapel under a striking double spiral staircase.

The Sun King's military models, saved from the Louvre.

A surrealist timepiece by the artist of melting clocks.

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.

The very center of Paris is surrounded by a bevy of strange good luck rituals.

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