Intertwined, interspecies trees which locals believe can grant boons to lovers.

An 18th-century Spanish watchtower made entirely of seashell and concrete.

In this case, 'zero' marks the spot where the iconic Old Spanish Trail ends.

A tribute to Ponce de Leon's supposed quest for eternal youth.

17th century streets hidden under Edinburgh were once a breeding ground for the black death.

"Respectful to the dead, safe and sanitary to the living, dedicated to the Genius of Memory..."

The world's oldest surviving music hall was also once a freakshow.

The elaborate clockwork contraptions in this Scottish gallery create small worlds of whimsy and horror.

King Ludwig I's collection of beautiful women.

The headquarters of a secretive order is also a beautifully-designed park.

A giant chess set, minus the psychedelic drug trip.

A peculiar mansion built by the troubled heir to the Winchester Rifle Company fortune.

An extensive collection of ancient Egyptian artifacts and mummies.

Built in 1870 at the bridge that connected Buda and Pest, this spectacular incline railway was almost lost forever during World War II.

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

The seawater playground of gilded-era San Francisco burned to the ground in 1966.

San Francisco's newly reopened hands-on science museum.

A collection of 20th-century automata, penny arcade games, and musical contraptions.

Scotland's oldest medieval bridge is also among the last reminders of early medieval Aberdeen.

The remains of a grand castle that may have inspired Bram Stoker's Dracula.

The ruins of this gorgeous clifftop castle look like something from a fantasy novel.

A glacial pothole was once a hideout for a notorious Scottish outlaw.