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

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

A battle between nature and architecture in the Cambodian jungle.

5,000 skulls in memorial to those killed by the Khmer Rouge.

Khmer Rouge's high security prison.

For centuries young Thai men used this Giant Swing as a slingshot to heaven.

Bangkok celebrated its shifting monarchy with a militaristic homage to democracy.

Macabre astrological automaton clock dating to the late 1400s.

From Austrians to Nazis to Soviets, this historic Budapest fortress has a history as complex as the city itself.

A misnamed well, with a deep dark past.

The place where World War I began.

Oriental bazaar in the heart of Sarajevo.

These historic defenses ensured the city within would survive hundreds of years of occupations, sieges, and invasions.

What happens when you cross a mayor and a painter?

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

This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

Where commuters walk through remnants of an ancient Greek necropolis.

Swarms of dainty flying insects swarm into the Petaloudes Valley to get busy.

An empty relic of the Moscow Olympics crumbles away in Estonia's capital.

A subterranean house of worship carved right out of the bedrock.

Longest road tunnel in the world features an air treatment plant and the illusion of daylight.

Copenhagen's celebrated theme park and gardens.

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

A little sculpture with a large wardrobe.