Once the home of a hermetic monk, this cave now houses a small church.

There aren't too many operational funiculars around, but Pittsburgh has two!

Thousands of coffin-like pillars make up this controversial Holocaust memorial.

Mysterious rocks that ring musically when struck.

A museum of carnival attractions where you are invited to ride the rides.

The history of radiation is on safe display at the foot of a radiation science laboratory.

This unreal Portuguese palace looks as though it's made from a pile of different castles.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

Catering to broken dolls for almost 200 years, this repair shop is now a charnel house of doll parts.

A cluttered and astounding collection of antiquities and curiosities.

This ancient Roman bridge and aqueduct still stands as a wonder of classical construction.

There has been an astronomical clock on this spot since the 14th century.

Lie in a hammock where George Washington stood.

Behind a bodega is a small museum of relics and ephemera showcasing the history of New York.

A Collegiate Gothic quadrangle that surrounds an 18th century secondary school whose financing came from the likes of Alexander Hamilton and Aaron Burr, among others.

One woman's decades-long obsession with the "La Fée Verte."

The ruins of a Duke's bucolic dream, where camels once roamed alongside "Dutch" windmills and faux-Italian vineyards.

Down a cobblestone alleyway is a museum dedicated to Romanticism, with a secret garden.

The celebrated eyesore created by starry-eyed sweethearts.

What's left of the ruins of the 1893 Columbian Exhibition, or World's Fair, also known as the White City.

This abstract sculpture is rumored to cast a hammer-and-sickle shadow once a year.

This bronze sculpture on a former squash court marks the secret origins of the Atomic Age.

This massive stained-glass masterpiece is thought to be the largest Tiffany dome in existence.

The site of a concentration camp where inmates were made to take part in one of the largest counterfeiting operations in history is now hauntingly empty.