The tunnel, built by volunteers in 1969, is known as "Beijing's Underground Great Wall," said Wang Junliang, an official at Qianmen's community labor service management center, which manages the tunnel.

"Most native Beijingers dug tunnels at home in the four downtown districts of Dongcheng, Xicheng, Chongwen and Xuanwu in those years," said Wang. "But most tunnels were just around three meters deep and were filled up over the past decades."

Except for the "Underground Great Wall" in Chongwen District in the southeastern part of the city proper, which encircles more than 1,000 square meters and links to several downtown subway stations today, he said.

The underground tunnel is 2.5 meters high and has two exits, one leading to a lane in Qianmen community and the other to the Temple of Heaven where Chinese emperors used to pray for plentiful harvests, said Wang.

"It was designed with many other exits but most of them have been blocked by buildings over the past years," he told Xinhua in an interview Wednesday.

He said the narrowest sections of the tunnel allow three people to walk side by side and in its widest parts, even a jeep can drive through.

Management has decided to open the tunnel only to individuals and small tour groups with five people or less for safety considerations. A trip into the tunnel costs 20 yuan (US$2.4) for adults and 10 for children.

Prior to its opening to tourists, the tunnel was decorated with old black-and-white photos featuring voluntary defense builders, portraits of the 10 marshals of the Chinese People's Liberation Army (PLA) named in 1955, outfits used by veteran soldiers in the 1960s and real size statues of former PLA men.

Underground tunnels, which linked every household in the neighborhood and ensured flexible maneuvers for attacks, defense and retreat, played an important role during China's war of resistance to Japanese invasion between 1937 and 1945. The two best known tunnels are located in Jiaozhuanghu village in the outskirts of Beijing and Ranzhuang village in neighboring Hebei Province.

Working on the tunnels remained popular for two decades after the People's Republic was founded in 1949, when the nation was still threatened by war.

Most of the surviving defense works have become tourist destinations and been listed as bases of patriotic education in a nationwide campaign to boost "red tourism" at former revolutionary bases. The campaign was launched in 2004 and is expected to last until 2010.

(Xinhua News Agency April 7, 2005)