A plaque marks the underground site of one of London's "lost rivers."

A commemorative plaque at the door pays tribute to an "American Patriot" known for his betrayal.

A story of cutlasses carelessly carving a celibate centenarian's cemetery stone.

This ancient Egyptian obelisk still bears the wounds of World War I.

The Great Fire of London and the regulation of one-way streets both started in this alley.

Op-art architecture designed for happiness.

This series of Baroque passageways in Vienna's cultural center mix old architecture with modern art.

Baroque celebration of the end of the Great Plague of Vienna.

A silly medieval mural preserved on the side of a Viennese house.

Vienna's diversity-themed traffic lights were inspired by the Eurovision Song Contest.

This Budapest bar allows drinkers to leave their mark on the walls, floor, and even ceiling.

A triumphant marble and bronze fountain depicting a 15th-century Hungarian king and his hunting party.

The true meaning behind this sculpture remains unknown.

A scene from one of Hungary's most famous novels.

The holes in this wall provide a glimpse into Jewish life in Budapest, both past and present.

This sculpture honors the man who was known as the "Righteous Among the Nations."

From cartoon characters to tiny tanks, a guerilla sculptor's little bronze statues are hidden throughout the city of Budapest.

On Gellért Hill, this statue depicts the tragic tale of lovers divided by the Danube.

The Hungarian biochemist whose research helped develop mRNA-based vaccines for Covid-19.

The remains of this misplaced church were moved here stone by stone.

Madrid's last horchata kiosk is a blue-and-white beacon of refreshment.

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

The remains of the second-oldest zoo in Europe can be seen within these library gardens.

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