This macabre masterpiece of a mural is one of Francisco Goya's "Black Paintings."

The earliest known map to show America, discovered by accident at a Paris bookshop.

The only urban monument in the world designed by the great surrealist painter Salvador Dalí.

Commonly acknowledged as the only public monument to the Devil himself.

Over two centuries old and counting, Madrid's massive botanical garden contains one of Europe's only desert environments.

A lush indoor jungle fills this bustling Madrid transportation hub.

Madrid's romantically ornate crystal palace has been offering shelter to plants and art for over a century.

A beautifully eclectic mix of architectural styles.

An ancient passage filled with stalls selling used books, once frequented by Vincent Van Gogh.

The attic of a four-century-old canal house hides a clandestine church.

An overgrown and largely forgotten cemetery lies hidden within the outskirts of Amsterdam.

The last of Amsterdam's original sea level markers remaining in place.

A Portuguese Jewish cemetery filled with stunning grave monuments that date back to 1614.

This subterranean studio is filled with fascinating kinetic art.

This museum inside Amsterdam's largest cemetery explores how people deal with death.

This massive mural by famed pop-artist Keith Haring was hidden for almost 30 years until its 2018 rediscovery.

The former headquarters of history's oldest megacorporation.

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

An astonishingly accurate water clock that doubles as an hourly spectacle in this Berlin shopping area.

The "Greatest Sewer" of ancient Rome is one of the oldest sewer systems in the world, and is still in use.

A preserved oak tree about 3,500 years old found in Riga, Latvia.

One thousand trees were planted in Norway to be used to print books a century from now.

Cold storage for agricultural biodiversity.

On the highest peak in the Harz Mountains, science and the occult faced off in a failed attempt to turn a goat into a boy.