Twenty-three trees, each paired with a basalt stone, line a street in Chelsea, continuing an urban project started by German Fluxus artist Joseph Beuys.

These banned cigarette vending machines now sell little pieces of pocket-sized art.

Famed for its pie, this eatery has a hidden tunnel that allowed Catholics to secretly walk to church during the Reformation.

Seven mini rowhouses fill the gap between 54 and 70 Westerstraat.

This cheese shop also houses a museum devoted to Dutch dairy.

Tucked in the back of a flower shop, its collection details the fascinating history of the Netherlands's iconic symbol.

Three connected pink triangles memorialize persecuted gays and lesbians throughout history.

A set of seven houses, each built in a style that represents a European country.

In the days before house numbers, these colorful signs held clues about various buildings' purposes.

A Dutch passageway's artistic, aquatic-themed makeover pays tribute to the capital city's famed waterways.

This historic Amsterdam bar used to accept sailor's monkeys as payment.

This bird-loving brewery is situated in an old municipal bathhouse, nestled beside a 300-year-old windmill.

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

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

A poem by Arthur Rimbaud is inscribed on the wall of a street that, while it is only one block long, plays a key role in multiple novels.

This 18th-century sundial was designed to calculate the date of Easter each year.

An unusual number plate signifies the building's saucy past.

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

This frog-themed restaurant was frequented by Picasso, Saint-Exupéry, and more.

The approximate spot where the last Grand Master of the Knights Templar was put to death.

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

A surrealist timepiece by the artist of melting clocks.

19th century pendulum and a clock restored by a rogue group of guerilla artists.

This Parisian café sticks almost exclusively to an ethos of reuse.