The ancient necropolis houses the immense rock-cut tombs of four Persian kings.

Hydraulic systems in an ancient underground Iranian city.

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

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

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.

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

This ruined fortress was the stronghold for a persecuted medieval leader and his infamous Assassins.

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

Iran's colorful terraces are a rare geological masterpiece.

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

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

The largest dam in the world and the site of a potential disaster.

The remains of an ancient city-state along the Silk Road.

This ancient Silk Road outpost overlooking the Wakhan Valley is miraculously still standing.

This dark, damp, perilous tunnel is the only passage from north to south Tajikistan.

A Lycian city of the dead carved into the hillside of Southern Turkey, complete with startlingly human touches.

A deadly ancient portal to the underworld.

This famous city eluded concrete detection until the early 2000's.

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

These tombs were built into the side of a mountain so that ancient angels could reach the dead.

Roman ruins top white travertine terraces formed by ancient hot springs.

In this historic region, homes and churches are carved into ancient volcanic rock formations.