It's one of Beijing's most fascinating yet least advertised attractions - A vast underground city beneath Beijing, built back in the Cultural Revolution and able to keep millions of Beijingers safe from nuclear attack. As the Sino-Soviet split worsened in the late 1960s, Chairman Mao and his then-heir-apparent Lin Biao stepped up construction of Beijing's bomb shelter complex out of fear of a Soviet attack. Tunnels were hewn out of the rock at depths of 10 meters and almost entirely by hand labor.

A labyrinth of tunnels and disused rooms still stretch for an unknown distance beneath the city streets. Few Beijing residents realize (and even fewer tourists) that all this lies just a few meters under your feet wherever you are in the heart of modern Beijing. The next time you parade around Tiananmen Square, or across the expanse in the Forbidden City, picture what lies beneath.

This underground city was stocked with food, fresh water, medical supplies and armaments. Elaborate ventilation systems were installed, as well as gas - and waterproof hatches which would supposedly protect Beijingers from chemical attack and radioactive fallout. Entrances to the Underground City could be found in neighborhoods all over central Beijing - There are no exact official figures as to how far the mostly hand-dug tunnels stretch, but they reportedly link all sides of central Beijing, from Xidan and Xuanwumen to Qianmen and Chongwen districts and even the Western Hills. Supposedly, some three hundred thousand could get below within minutes of an air raid warning and survive there for four months.

Probably the best place to see the Underground City today is an entrance near Qianmen. Run by the Tourism Bureau, this section is well lit and fairly extensive. You can take a 20-minute stroll through a circuit that lies about 10 meters underground. Comprised of tunnels three to four meters wide, it contains a hospital, classrooms and even a barbershop. Numerous narrower side passages, some of them reaching quite far down, offered tantalizing detours, but you are discouraged from exploring them.

You will walk past pictures of Marx, Engels, Lenin and Stalin. You will read slogans from the Cultural Revolution about struggle and war preparedness, murals of proletarian heroes rendered in vintage Socialist Realism, a ceramic bust of The Great Helmsman. And you may also emerge into a brightly-lit underground silk workshop. The tunnel on the exit side of the workshop was done up in imitation Buddhist frescoes evoking the Fahai Temple and Dunhuang, and led to a gaudily festooned altar to the Bodhisattva Guanyin.

Jacket and flashlight is suggested.

More tours are available upon request.