A Pythagorean funhouse that tries, successfully, to prove that math is the coolest thing ever.

The feral felines of Roosevelt Island have a small army of allies and an abandoned hospital all to themselves.

A semi-scholarly approach to sex.

A tiny museum housed in a New York freight elevator specializes in the "overlooked, dismissed, or ignored."

A crumbling hospital from the 1850s on Roosevelt Island.

Arrr! The most authentic collection of pirate artifacts in the world... matey.

A giant bronze coil of feces is both a tribute to doggie defecation and a reminder to pick it up.

This whimsical Oz-themed park had a wonderful impact on the surrounding neighborhood.

Cleveland's giant "free" stamp is a nod to the Civil War, but was misinterpreted for years.

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

This unique bridge curls up like a caterpillar to let boats pass and then unfurls again to span a small canal.

The remains of the great moral philosopher reside in a university in London.

A student driver's nightmare.

Banksy gives themself artistic license with this piece of London street art.

The popularity of Sherlock Holmes led to the creation of his fictional address, turning the orderly London street numbers askew.

A kaleidoscopic warehouse-maze of handmade neon signs.

This semi-secret storybook hedge maze is also the oldest garden in the city.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

Inside a former cabaret, seven floors of erotic art.

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

"In the Dark" Restaurant in Paris offers dinner in complete darkness.

A favorite Paris bar for U.S. expats, including Gershwin, Hemingway, and James Bond.

High atop the Eiffel Tower is a small apartment built exclusively to entertain the science elite and make the rest of Paris jealous.

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