If a glacial river suddenly diving into a sheer chasm via a dramatic, multi-stage waterfall isn't peak Iceland, it's certainly close.

This valley of hot springs and boiling mud pots is home to the record-holding "Geysir," which originated the English word.

This fantastical waterfall is hidden in a cave located in a cracked cliff.

One of the tallest buildings in Iceland, and perhaps, the most visually impressive.

This eye-popping Icelandic crater lake is surrounded by red volcanic rock.

Medicinal spa created from the mineral-rich runoff of a geothermal power plant

A reconstructed medieval gateway that was the magnificent entrance to the capital city dating back to 1037.

This derelict superstructure was a very important warning system for the Soviet military.

One of the most poignant ruins of the Chornobyl nuclear disaster, the local football team's stadium has been quickly reclaimed by nature.

This attraction was abandoned after the Chornobyl disaster.

The ghost town left by the worst nuclear disaster of all time is being taken over by nature and urban explorers.

The largest prehistoric ruins south of the Sahara, once a powerful center of international trade.

Part modern art project, part traditional chapel, this see-through church is only substantial from the right angle.

Rare wooden escalators lead deep down into an otherwise staggeringly monotonous tiled tunnel.

A king's pet, a pope's gift, an artist's inspiration, and a tragic shipwreck.

Located in the thermoelectric factory that once powered the entire city, this Portuguese museum is shockingly fascinating.

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.

This unreal Portuguese palace looks as though it's made from a pile of different castles.

Elaborately carved to showcase the glorious wealth that the age of exploration brought to the Portuguese empire.

Legacy of the earthquake that nearly wiped Lisbon off the face of the Earth.

This Industrial Age architectural and engineering gem helps visitors and residents alike traverse Lisbon, “The City of Seven Hills.”

An expansive complex of subterranean tunnels is all that remains of one of Europe's most formidable medieval fortresses.