The secret city built by the Manhattan Project.

Once decrepit and slated for demolition, now one of the longest pedestrian bridges in the world.

One of the Cemestos prefab homes built to secretly house thousands of Manhattan Project workers.

One person's lost luggage is another person's treasure.

Once one of the largest producers of pig iron in the world.

A miniature city built by a single hunchbacked monk.

Better known as the "Body Farm," this unique research facility has been studying how human bodies break down since the 1980s.

A Surreal flight of architectural fancy in Vietnam's Central Highlands.

This striking landscape in northern Vietnam contains both geological and archaeological wonders.

The notorious "Hanoi Hilton" where Vietnamese colonial subjects and later American POWs, including John McCain, were imprisoned.

Ha Long Bay's "Cave of Surprises" houses a popular phallic rock formation.

This cavern was used as a hidden hospital and safe house during the Vietnam War.

World's largest cave was only discovered in 1991, and now offers tours to the public.

This network of tunnels housed an entire village for years, and even had a hall for screening movies.

This bridge is embedded with a giant steel dragon that breathes fire from its mouth.

This Vietnamese hell cave lets visitors take a walk through a devilish underworld full of demons.

Home to what locals claim is the largest whale skeleton in Southeast Asia, which is worshiped yearly.

One of the world's southernmost bars.

This abandoned mining village was predicted to resist decay longer than any other modern human settlement.

The world's second-largest excavated hole.

On Japan's Tashirojima Island, cats are king.

Two islands just 4 km apart separated by an International Border and Date Line.

The birthplace of Karl Marx is now a museum dedicated to the communist revolutionary's life and work.

Abandoned castle was once a grand example of Russian privilege, built exclusively to win a frivolous bet between noblemen.