This hunter-gatherer architecture is believed to be the oldest religious complex known.

Keshwa chaca, among the last handwoven Incan bridges, crosses Apurimac Canyon in Peru.

Hundreds of thousands of concrete bunkers crowd Albania long after the fall of Communism.

A naturally beautiful, seemingly bottomless deep blue spring.

Monasteries on rock pillars, once accessible only by frayed ropes.

Ancient Greek oracle of the dead.

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

Hideout of thieves, monks, and goat-footed gods.

A harrowing trail up a mile-high mountain.

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

A lake with hundreds of ancient skeletons surrounding it. The surprise is what killed them.

This complex of vertically-excavated Buddhist, Jain, and Hindu monolithic temples in India's Maharashtra providence illustrates a spirit of tolerance characteristic of ancient India.

Rock-cut cave complex filled with ancient Buddhist artwork.

Where cemeteries are carved into the side of cliffs and infants are buried in the hollows of trees.

Hundreds of wooden coffins dangle from cliffs and caves in the Philippines.

Hindu temple of the dead home to hundreds of long-tailed macaques.

Smoked mummies housed in mountainside caves.

Intensely colorful calcite pools in Southern China.

Snow-capped peaks, colorful waterfalls and stunning vistas on the edge of the Himalayas.

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

A natural arch offers panoramic views of Yangshuo's karst hills.

A mud volcano in Indonesia spews out 50,000 cubic meters of mud every day.

A centuries-old fortress city lies in ruin.

Centuries-old bridges grown from tangled roots.