A historic trade hub teeming with gorgeous architecture, colorful goods, and vibrant designs.

One of the largest and oldest caravansaries in Persia.

The hottest, driest, and most scenic desert on Earth.

These little castles each held thousands of pigeons.

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

This vast, water-filled underground labyrinth can only be toured by boat.

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

One of the world's largest salt caves is filled with fragile salt sculptures, salt rivers, and huge salt megadomes.

A sophisticated astronomical tower built by one of the greatest Persian scholars of the Islamic Golden Age.

Hydraulic systems in an ancient underground Iranian city.

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

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

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

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

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

Iran's colorful terraces are a rare geological masterpiece.

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

A rare pod of derelict midcentury Futuro and Venturo houses lines a semi-abandoned beachfront resort outside Taipei.

The underground hideout of a Japanese soldier for whom World War II ended in 1972.

Centuries before the modern seismograph, Armenian monks measured quakes with this tilting pillar.

A rapidly disappearing glacier filled with extinct grasshoppers, perfectly preserved in the ice.

An ancient instrument used to measure the waters of the Nile so Egyptian farmers would know whether to expect famine or flood.

An architect transformed this abandoned cement factory into his castle-like workshop.

Martin Bricelj Baraga's monolithic sculpture measures the blueness of the sky, and changes color to match it.