From the air, lines of holes across Iran's deserts look like craters. Each one is a shaft dropping into a single hand-dug tunnel: a qanat.

• ✓UNESCO WHC, The Persian Qanat (1506)
• ✓FAO GIAHS, Iran qanat-based saffron system

These holes in Iran's desert look like craters. They're not. Each one drops into the same tunnel, dug by hand. It's a qanat, and it carries water. It taps groundwater under higher land, then slopes gently down toward the farms. Gravity does the work. No pump. Buried, the water loses far less to evaporation. The shafts let diggers haul out the soil, and let crews climb back down to clear blockages. Farmers here have drawn water this way for more than 2,500 years. Today it grows saffron on land with no river. And all of it flows under these holes in the desert.