A 19th-century subterranean reservoir repurposed as a contemporary art cave.

The old observatory in Copenhagen has a spiral corridor used as a racetrack.

Danish tourist destination well known for open stalls where vendors sell marijuana on the street.

An ultra-modern diversity park in Denmark has turned an entire city block electric pink.

Sweden's oldest animated sign is still lighting up the skyline today.

It houses the remains of a 17th-century version of the Titanic.

Tucked away amidst some of the most famous addresses in the world is New York’s only fraction of a street.

Wine bottle sculpture with a ship's stateroom inside.

Site of a classic 19th-century physics experiment to prove the earth is rotating.

A horde of stray cats rule in this secluded Parisian cemetery under a bridge.

France's national museum of scientific and industrial instruments.

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

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

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

The anatomical-pathological collection of a man who changed surgery.

Yo, Adrian!

This elaborate towering structure was once famed for its revolutionary height.

Ant sculptures march up the side of what used to be an iconic spot in punk rock lore.

The world’s first penitentiary, meant to be humane, drove men insane.

America's most famous museum of medical oddities is home to the remains of Albert Einstein's brain.

Beautiful mosaics cover the first stations opened on New York City's newest subway line.

The name of this tiny pocket park tucked between two buildings on Manhattan's Upper West Side is Latin for its location: "seventy-one."

A dark patch of the ceiling at Grand Central Terminal which was not restored is still stained brown by tobacco.

A Manhattan office building is home to the world’s largest chess board.