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

Largest cave system in Africa.

A sulfuric hellscape in southern Italy.

This large round boulder is said to emit spiritual power, but it may just be magnets.

A deadly ancient portal to the underworld.

Superstitious? Discover the witchy side of Mexico through its largest esoteric market.

The notorious headquarters of a corrupt political machine.

The stones of this Incan wall complex fit together so well you couldn't fit a piece of paper between some of them.

Elevated freight railway turned wildly successful urban park.

It houses the remains of a 17th-century version of the Titanic.

Every equinox this Maya pyramid puts on a spooky ancient light show.

A walk through the historic city center, under the streets of Seattle.

A battle between nature and architecture in the Cambodian jungle.

Where commuters walk through remnants of an ancient Greek necropolis.

Thousands of exquisitely carved stone water storage wells, hundreds of stone steps fill this exquisite medieval stepwell.

A Turkish ghost town abandoned in a population exchange with Greece.

Virgil's many-mouthed gateway to the underworld.

An ancient capital city that dates back 3,000 years old and harbors many surprises.

The largest stone moai on Rapa Nui.

An Aztec temple, the largest man-made pyramid in the world, sits buried in earth with a Spanish church set on top.

A wooden hut from the Heroic Age of Antarctic Exploration.

The last moments of the ill-fated Pompeiians, frozen forever in plaster.

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

An underground paleo-Christian burial site composed of the remains of several cemeteries and Basilicas.