A half-mile-long stretch of medieval forts built after a devastating pirate attack persists amid the modern port city.

Original cabaret handbills, posters, and feline artwork are a purrfect highlight of the Museum of Montmartre.

An unexpected Easter egg lurks in the background of a cherub wall relief at the Breakers mansion.

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

Six ravens are kept captive (but well-fed) at the Tower of London to prevent the fall of the Crown.

A 16th-century fountain marks the site of a lost medieval cemetery once filled with mass graves.

Affectionately known as "Lord Bot," this historic statue has a cult social media following and rightly claims to be “the most metal inhabitant of the Wren Yard.”

A forgotten relic from New York's bygone trolley system hides in plain sight under a bridge.

The oldest and smallest cemetery in Paris is only open to the public twice a year.

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.

Exquisite wall sculptures carved in secret by an early quarryman in an obscure corner of the Paris Catacombs.

There's a piece of New York City transportation history hidden in plain sight at a Manhattan subway stop.

The sounds of the world's largest fully functioning pipe organ dazzle shoppers at a Philadelphia Macy's.

Stripes of human ashes cover a back lawn in the most sought-after burial grounds in Paris.

The watery entrance for condemned prisoners heading to the Tower of London is still visible along the Thames.

The original toys that inspired the beloved children's stories are on display at the New York Public Library.

The upstairs reading room is packed with millions of rare books, literary manuscripts, and historical treasures.

Perhaps the most scandalous statue of America's first president.

A French artist's vague warning hangs over Belleville.

This nearly invisible wire transforms much of the city into one big, symbolic home on the holy day.

This banal Parisian entranceway is not what it seems.

Twelve grave-faced marble angels guard the emperor's tomb at Les Invalides.

This museum in a Paris apartment gives a unique look at the iconic French singer's life.

Peeing dogs guard the Roman hunting goddess atop a fountain at France’s Château de Fontainebleau.