This mountaintop lake bubbles and steams in a perpetual boil, thanks to its direct link to the Earth's interior.

The ancient water tanks remain some of the ruined city’s most beautiful architecture.

The remains of what was, not so long ago, the world's largest city.

Crumbling remnants of what was once a booming town full of silver.

Grotesque statues of figures from Buddhist hell haunt the temple's Sin Park.

Thanks to both terrific preservation and historic vandalism this ancient site is known as the "Heart of Neolithic Orkney."

The discovery of this Neolithic settlement, which contained a Stone Age "cathedral," threw archaeologists for a loop.

The courtyard of this small Marinid madrasa is a dazzling example of intricate Islamic architecture.

The largest madrasa in Morocco once housed more than 900 students within its exquisite walls.

The oldest known university in the world is in Fez, Morocco.

Fortune tellers, snake charmers, poets, and storytellers all gather on this historic square in Morocco.

God's Saharan sandbox of wrath.

Traditional 11th-century outdoor tannery.

Thousands of narrow alleyways in an ancient medieval city make up what's believed to be the world's largest car-free urban zone.

The other side is actually green.

World's largest film studio, where visitors tour the decaying sets that litter the harsh desert environment.

A fortified city, home to a remaining population of five families

Mosaics, storks, and brothels—this ancient city has it all.

Limestone caves in the Cambodian countryside, once the site of genocide, now a place of peaceful beauty.

A hidden church in a hidden courtyard tells the story of the Miracle of Amsterdam.

In the days before house numbers, these colorful signs held clues about various buildings' purposes.

Famed for its pie, this eatery has a hidden tunnel that allowed Catholics to secretly walk to church during the Reformation.

This bird-loving brewery is situated in an old municipal bathhouse, nestled beside a 300-year-old windmill.

Amsterdam's former hotspot for public executions and dissections.