Huge stone depressions which may have acted as an Incan agricultural experiment.

These steeply terraced ruins are a stop along the Inca Trail to Machu Picchu.

This remarkably well-preserved Incan city managed to survive the conquistadores.

Structure built from the skulls of vanquished foes.

Curious carved stones and bird-like wings are a symbol of Serbian resilience and freedom on the site of a WWII massacre.

A small marionette collection located within the dark cellars of an 11th-century Austrian castle.

Remnants of the 16th-century defensive wall still stand unassumingly within Edinburgh.

At just 51 feet and 10 inches long, it's the shortest street in England.

A magical place that lets you play in and explore the world of Studio Ghibli.

Cold War intelligence agents monitored communist embassies from an attic in a former pigeon coop.

The Roman Emperor's lost summer home and grotto full of enormous sculptures sit along the Italian seashore.

Although rarely used, there is still a hidden room for the royal family at the Stockholm central station.

Remnants of the rich history of fish salting in this ancient Mediterranean port town.

A book bound in the skin of an infamous criminal, along with countless other specimens.

A library where thousands of books explain how to avoid another Great Recession.

This impressive system of tanks was used to store drinking water as long as 2,000 years ago.

Legions of Roman soldiers bathed in this ancient spa complex under a Budapest transit station.

The body of an unidentified woman, visible through a glass coffin, was discovered by accident.

An abandoned gun-funded 19th century utopia.

An abandoned Depression-era zoo hidden just off the highway.

A modest museum in the final home of Italian poet and father of modern Italian, Francesco Petrarca.

A medieval fountain lined with 99 unique stone faces whose origins and meaning remain unknown.

The watery entrance for condemned prisoners heading to the Tower of London is still visible along the Thames.

The original film set of Luke Skywalker's Tatooine home from the 'Star Wars' trilogy.