A cave dwelling that was started by the Celts, expanded by monks, and finished by knights.

One of the greatest maze designer’s greatest mazes.

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

A subterranean shelter remains intact under a busy Paris railway station.

This French ghost town from World War II has been left as a memorial to German atrocities during World War II.

A surrealist timepiece by the artist of melting clocks.

This 1,300 year old monastery built atop a single rock was once only accessible depending on the whims of the tide.

Abandoned railway line circling the city of Paris.

Notorious artist squat renovated into legal studios.

France's most famous cemetery, with some of its most curious tombs.

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

A haunting collection of the vanished and disappearing natural world.

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

The oldest pub in Ireland may also be the oldest surviving bar in the entire world.

An 80-year-old plane tree is devouring an iron bench at Ireland's oldest law school.

One of Ireland's most infamous prisons for rebels including men, women and children.

One of the most popular megalithic sites in Ireland stands as a humbler version of Stonehenge.

An eccentric garden of sculptures crafted in India decorate an Irish green space dedicated to Alan Turing.

An Irish church where an 800-year-old mummy is reaching out of his coffin as if to shake hands.

This floating garden in the sky is straight out of a fairy tale, but the real thing is nothing short of magical.

The ancient tomb acts as a calendar that keeps perfect time.

This Irish show cave is said to have been the site of a Viking massacre that claimed 1,000 lives.

A theme park that suffered massive flooding during Katrina was abandoned, and now proves irresistible to trespassing explorers.

An homage to everyone's favorite prehistoric cartoon family.