Around 100,000 bodies are buried below the medieval headstones, many of which mark graves with multiple bodies stacked up to 12 deep.

Macabre astrological automaton clock dating to the late 1400s.

A fire station-turned-church-turned-museum dedicated to the work of seminal light artist Dan Flavin.

The world's longest known cave system.

Unique tower has outlasted a takeover of the company.

This railroad and oil tycoon's lavish estate now stands as a time capsule of the Gilded Age.

This historical swimming pool near Miami is emptied and refilled each day with naturally filtered water.

This spooky road cut through a mound of ancient coral might be haunted by a witch.

This war hero's old shop remembers the fine line between medicine and quackery during the Revolutionary War.

Home to secret Eastern Bloc spy equipment and the largest stretch of the original Berlin Wall outside of Germany.

Known as the "Hobbit Houses," these storybook homes look like they're straight out of the Shire.

Historic funicular railway, believed to be the shortest railroad in the world.

The legendary building that needed ghostly approval before being built.

This isn't your average roadway—it's actually a National Park and a transportation pioneer.

The Pentagon is so large that it was planned like a city, complete with internal highway infrastructure.

This lonely waterfront memorial to the men of the Titanic was erected by the "Women of America."

A crumbling hospital from the 1850s on Roosevelt Island.

Site of the first pathological and bacteriological research facility in the United States.

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

One of only two commuter aerial tramways in the United States.

A burnt orange monolithic dome structure perched on a hillside near Interstate 280.

A storybook European village in Berkeley.

The Laureates here get something even more coveted than a Nobel Prize: free parking for life.

The century-old bell and clock tower at UC Berkeley is the third-tallest in the world, and has fossils.