Venice's island of the dead.

Go inside to really appreciate this 500-year-old technological masterpiece.

A former waterfront market is now in the center of town due to some interesting Boston engineering.

This cemetery has graves dating back to the 17th century, including the city's oldest carved tombstone and an ominous cryptogram.

The most confusing clock in New York.

An inspired museum dedicated to the patron saint of enslaved people, inside the cloisters where he lived and died.

This Costa Rican topiary park is a surreal garden of unearthly delights.

This Costa Rican chapel is the most metal church in the world, literally.

The sister plane of the C-123 shot down during the Iran-Contra Affair has found a new purpose in retirement.

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

One of England's most famous churches hides a pair of little known architectural treasures.

One of the few standing Roman lighthouses and a labyrinth of tunnels are a couple of the secrets at this historic castle.

Climb inside an iron crystal magnified 165 billion times its normal size.

This fairytale castle was built as a show of power but was nearly torn down thanks to its history of torture.

This one-time health resort was used by aristocrats around the world.

A whimsical bridge adorned with decorative dragons.

This abandoned Slovenian military barracks has become a punky-political art squat.

This Slovak bridge is known both for its connection to a national uprising and its UFO-shaped eatery.

A trail of iron footwear stands as a monument to the thousands executed along this riverbank during WWII.

Destroyed Serbian army headquarters sits half crumbled in a largely revitalized Belgrade.

Nikola Tesla's ashes are held in a golden sphere, surrounded by his works.

A misnamed well, with a deep dark past.

A towering spire in the fortress of Kalemegdan honors the victorious armies of Serbia during their struggles against the Ottoman Empire.

A giant portrait of an ancient king looms over the river.