Hundreds of secret cabinets built into the walls of legendary poisoner's private work room.

A chapel on a volcanic core, marking the end of a successful journey.

The artist and his brother are buried in a landscape straight out of a van Gogh painting.

The world's largest reflecting pool is just two centimeters deep.

An ancient monastery, a locked room, and a mysterious book heist.

One of the oldest masonic museums in Paris.

A self-built mosaic house and sculpture park.

One woman's decades-long obsession with the "La Fée Verte."

Museum in a swimming pool where the water still flows.

This French castle is said to have once held the Holy Grail but is now a gorgeous mountaintop ruin.

A French valley with forests so lush it was nicknamed "the Small Amazonia of the Pyrenees."

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

This innocuous-seeming building is actually the remnant of a major wartime brothel.

Architect Le Corbusier built his friend a cubist house to match his impressive collection of cubist art.

This ancient Roman bridge and aqueduct still stands as a wonder of classical construction.

Despite being considered a thoroughly American sport, basketball's oldest surviving playing field is found in the basement of a Paris YMCA.

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.

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

A beautiful and classically designed villa, with an hourly infestation of monsters.

A series of abstract, silly sculptures represent the works of a great modern classical composer.

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

An iconic and eccentric bar for "Manouche" Jazz music keeps expanding its space—and its influence.