The remarkable 2,000-year-old system allowed the desert cities of the Silk Road to flourish despite an unrelentingly arid environment. In the oasis cities of Turpan and Hami, 1,600 km (990 miles) of underground tunnels brought water—moved only by gravity—from melting snow at the base of the Heavenly Mountains. You can view the tunnels at several sites around the city. Most tour guides take visitors to the largely educational Karez Irrigation Museum. Despite being described as the "underground Great Wall," most visitors are completely underwhelmed by what are essentially narrow dirt tunnels.
888 Xincheng Lu, on the city's western outskirts, Turpan, 838000, China