London's smallest police station is barely the size of a phone booth.

An unusual ode to the late Irish playwright, complete with a squiggly bust and coffin-shaped bench.

An archway adorned with vulnerable flora and fauna.

A living memorial to the trees London lost during the Great Storm of 1987.

One of America's founding fathers lived in this London lodging between 1757 and 1775.

The bronze uniforms commemorate the vital role of women during World War II.

A statue of the legendary Celtic warrior queen who fought the Roman invaders stands in one of the cities she once destroyed.

The bar where "The Great Train Robbery" was planned was once a nexus of high society and low morals.

This striking statue brings a scene from the African savannah into central London.

A tiny replica of the iconic London landmark hides on the side of the steel structure.

A network of bells in the pubs and restaurants around Westminster alerts politicians when it's time to cast their votes.

The first green space constructed on an elevated viaduct.

A tribute shrine where the Space Invasion street art movement started.

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

A museum on the history of Paris, including a set of Napoleon's toiletries, Proust's room, and relics of the Revolution.

Notorious artist squat renovated into legal studios.

For more than a century, revolutionary graffiti has marked the wall of a Parisian church.

This charming cobbled backstreet is the most Instagramable street in Paris, much to the residents' annoyance.

Grab a life-changing ham sandwich at this former horse butchershop.

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

A commemorative plaque hides a door that leads down to the New York Public Library's underground book bunker.

Commemorating the spot where the famous scientist fed his pigeons.

Order a boozy baba au rhum at the oldest patisserie in Paris.

Underwater art project will double as a massive artificial coral reef to help regenerate the damaged ecosystem.