In the late 1960s, with the cold war at its peak and strained diplomatic relations between the US, Soviet Union and China, the Chinese built huge civil defense systems, especially in northern China. One of the remnants from this period is the Underground City. Today the Underground City is much like its counterpart above the surface - there are factories, warehouses, shops, hotels, theaters, rollerskating rinks and clinics. This subterranean city covers an area of 85 sq km and much of it was constructed by local citizens and volunteers under the guidance of the army. You can still visit some of the shelters that have not been converted into shops in the Qianmen area and can also view the telecommunications and ventilation systems.