By Viva Goldner (Beijing Weekend)
Updated: 2007-10-23 14:25

Deep below China's bustling heart lies a dank network of secret tunnels and purpose-built rooms that Chairman Mao Zedong once envisaged housing up to 40 per cent of the capital's residents in case of nuclear attack. Constructed between 1969 and 1979, the bomb shelter, known as the Underground City, was part of military strategy, dating from the Sino-Soviet border conflict over Zhenbao Island in Heilongjiang River, northeast China.

It was built by more than 300,000 residents, including some school children, using hand-held tools and materials sourced from Beijing's ancient city walls and towers.

Visitors can now explore part of the tunnels, which stretch for more than 30 kilometers beneath Beijing's center. From a discreet, shopfront entrance in a hutong not far from Tian'anmen Square, stairs lead down to the shelter, located between 8 and 18m underground.

An English-speaking guide leads guests through the low, narrow tunnels, pointing out sealed-off passages to Tian'anmen Square, which is ten minutes away, the Forbidden City, and the Temple of Heaven. There are also wider tunnels to accommodate vehicles.

At the start of the tour, our guide Daniel (pictured) tells us photos are forbidden, because the site is the protected property of the national defense department.

There is a cinema, a recreation area for seniors to play cards, and a reading room for youngsters, as well as a hospital that could accommodate 20 injured soldiers or civilians, and artillery stores. Though not on the approved underground "sight-seeing" route, the complex is also said to house shops and restaurants, schools, a grain and oil warehouse and even a roller-skating rink. Daniel says there are also "many kitchens and rooms" designed to house residents ordered underground, though these, too, are off-limits to visitors.

The tour does stop at the underground silk factory, housed in a large space that today serves as a State-owned shop selling silk quilts, garments and other items at reasonable prices.

Daniel says the government was concerned of potential diseases risks, such as rheumatism, should people be forced to live in the cold, wet conditions of the underground city. Today, water drips down from above, and a moldy smell permeates. Fresh air vents were also constructed in several places throughout the complex, allowing natural light to filter down from the streets above.

The Underground City is sometimes also called the Underground Great Wall, for its role in military defense strategy. Our guide says similar bomb shelters exist in China's other cities, connected by tunnels and stretching for a distance as long as the Great Wall itself.

The tour covers just a small section of the Beijing tunnels, which cover an area of 85 square kilometers, and are said to link all areas of the city, from Xidan and Xuanwumen to Qianmen and Chongwen Districts. But it provides a fascinating glimpse into what could have been a secret metropolis, as well as the chance to learn something more of China's military history.

Location: 62 West Damochang Street, Qianmen
Price: 20 yuan
Tel: 010- 6702-2657