Once America's longest-manned military fort, now an abandoned hulk.

A crumbling hospital from the 1850s on Roosevelt Island.

This hidden library of physiological ephemera contains centuries worth of knowledge on the vim and viscera of the human body.

Avoid gangster interaction while window-shopping.

The walls are decorated with whimsical murals painted by the creator of the Madeline franchise.

This mosaic dedicated to John Lennon was tended for years by a Beatles super-fan.

Mysterious 500-year-old tapestries depict a unicorn hunt.

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

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

Arcadia is home to a haven for nature geeks and 80s TV lovers alike.

Explore the atmospheric ruins of an abandoned convent in the dense forests of Mexico's first national park.

This small museum displays a collection of outsider art and scale models of past "treatments" for mental illness.

150-year-old satirical tableaus made from stuffed frogs.

These spooky and unusual stone formations create an underworldly landscape.

This lovely little bridge hidden in a Switzerland gorge is essentially a fairytale.

Caves famous for the dragon-slaying saint who lived there.

Tables of secondhand books fill the inner courtyard of this 17th-century stock exchange.

A sanctuary for wolves in a community which once trembled in fear of the murderous "Beast of Gévaudan."

This memorial commemorating fallen Swiss Guards of the French Revolution has been called the saddest stone in the world.

A nearly 500-year-old sculpture depicts a man eating a sack of babies, and no one is sure why.

Long-abandoned art nouveau baths beneath Milan's Piazza Oberdan.

A Milanese café entirely designed by the American director Wes Anderson.

A kaleidoscopic warehouse-maze of handmade neon signs.

London's creepiest cemetery was once the site of dueling magicians and mobs of stake-carrying vampire hunters.