Where royalty waits in the height of luxury.

A rare tour of an aristocrat's private home reveals valuable 17th-century paintings from artists like Rembrandt.

A beautifully eclectic mix of architectural styles.

A line number in Amsterdam that will likely never be used again due to its tragic history.

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

London's last remaining public soapbox site has seen speeches from Karl Marx, Vladmir Lenin, and George Orwell.

A discarded movie prop that was the original monolith for "2001: A Space Odyssey."

Under the right conditions, rocks will move across this dry lakebed, leaving trails behind them.

An odd museum dedicated to French fakes.

The narrowest street in Paris.

The tradition of open-air secondhand and antiquarian bookselling in Paris dates back to the Renaissance.

An off-the-beaten-path boutique stuffed with an eclectic collection of upcycled goods.

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

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

A horde of stray cats rule in this secluded Parisian cemetery under a bridge.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

This frog-themed restaurant was frequented by Picasso, Saint-Exupéry, and more.

The lantern carried by the infamous Guy Fawkes when he was arrested while attempting to blow the houses of Parliament and the King of England to smithereens

The subterranean "lake" below the Paris opera house inspired the Phantom of the Opera's lair.

The curious underground history of keeping Paris clean.

One of Jeff Koons’s largest sculptures and his first commemorative work.

The John Snow Memorial marks the epicenter of London's 1854 cholera epidemic.

An arsenic-filled pool in the Grand Canyon takes on the appearance of a giant, overflowing pumpkin.

The final resting place of soldiers' loyal canine companions.