New York City's smallest piece of private property.

Whisper secrets in a busy station only to be heard on the other side of this acoustic arch.

The one-stop shop for all of your superhero (or evil arch-nemesis) needs.

A semi-scholarly approach to sex.

Elevated freight railway turned wildly successful urban park.

Manhattan’s Battery Park has a whimsical carousel full of spinning, glowing fish.

A mysterious chasm in the heart of the ancient Roman Forum, the Lacus Curtius was once believed to be a gateway to hell.

Rome's semi-secret peephole vista is also a former Crusader stronghold.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

This Polish cave has housed a dragon, a brothel, and an enduring legend.

The celebrated eyesore created by starry-eyed sweethearts.

The video game-themed street art first popped up in the French city.

A Parisian exterminator's shop whose storefront displays stuffed rats hanging from traps.

The first green space constructed on an elevated viaduct.

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

A marine aquarium with an astounding variety of fish hides in the basement beneath the famous Palm House.

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

This once-controversial and slightly confusing statue of Achilles was built out of captured cannons.

A tribute to all the green-thumbed workers who tend London’s public parks and gardens.

A sculpture of a famous ape who was once a beloved household name in London.

Legend says these colorful, invasive residents are the descendants of birds released by Jimi Hendrix.

Where's a guy to go after a long, hard day at work?

The Tudor-style cottage in the middle of the square is not quite what it seems.

A unique tribute to the millions of animals who served and died for the British military.