Putrefaction plateaus in Iran, where the dead were sent for decontamination before going to their final resting place.

A 1,500-year-old, 3-story subterranean city where ancient Persians took refuge in times of war.

This beautiful system of tunnels built into natural rock serves as a centuries old plumbing system.

The vertical-axis windmills of ancient Persia have been grinding flour for 1,000 years and counting.

Modern-day cave dwellers carve elaborate homes out of volcanic debris.

Ancient structures used to make and preserve ice in the deserts of Persia.

Hydraulic systems in an ancient underground Iranian city.

A spectacular rainbow of stained glass makes the "Pink Mosque" one of the most beautiful in Iran.

Mirrors and glass shards cover every inch of this arrestingly beautiful mosque.

The palace of the King of Kings, burned by Alexander the Great.

Iran's colorful terraces are a rare geological masterpiece.

Skyscraper powered by wind turbines attached between its towers.

This centuries-old tree tells an unusual tale of vegetation and fertility in the desert.

One of only two civilian settlements in the desolate lands of chilly Antarctica.

Southern Ocean waters and glacial forces transform the Antarctic ice into these stunning bridges and caves.

Nimrod Polar Expedition base, and home to hundred-year-old frozen whisky.

The best place to send your postcards home from Antarctica.

Russian Orthodox church built on an Antarctic island.

One of the world's southernmost bars.

Natural time capsule containing an alien ecosystem.

These naturally balancing rocks were pictured on every Zimbabwean banknote, up to the 100 trillion-dollar note.

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

A strangely forgotten claimant to the much contested title of "Source of the Nile."

Hidden dwellings in the cliffsides of North Togo used by local Moba tribes to evade 18th-century slave traders.