In the bitter coldness of Beiing's winter, going out sightseeing doesn't sound like a great idea for most, unless the destination is indoors.

So at this time of year, the Beijing Underground City, one of the city's most fascinating yet least advertised attractions, is one of the best choices.

Mind you, finding it is not easy, even for a native Chinese speaker. Though the address is specific enough, it doesn't really help as you wander through the nondescript hutong to the south of Tian'anmen Square. There are almost no door-plates for you to check if you're still on the right track, and asking directions from locals doesn't really help, sometimes making you feel less assured when they tell you: "Beijing Underground City? I don't think there is a place like that."

For more than 20 years, the bomb shelter complex just beneath the ancient capital's downtown area, has been virtually forgotten by local citizens, despite being well-known amongst foreigners since it officially opened in 2000. Few people living nearby seem aware of its existence.

But it is there. So if you really need to be assured, just check if you're in the Xidamochang Hutong. Keep heading east from Qianmen and near the end of the hutong lies the only confirmed entrance to a labyrinth of tunnels and disused rooms that still stretches for an unknown distance beneath the city streets.

The entrance looks like an ordinary small shop carrying the signs "Underground City" in both Chinese and English.

As my colleague and I jokingly complained about how hard it was to find the place, our guide said with a grin: "Just think about what it was originally built for."

He had a point. Beijing Underground City, a leftover from the Sino-Soviet border conflict in 1969 over Zhenbao Island in northeast China's Heilongjiang River, was dug on the orders of Chairman Mao so that the city's populace could disappear below ground within three minutes of an air raid warning.

Our guide claimed it took 40,000 workers and the best part of a decade to complete the complex. "Almost all of our fathers' generation in Beijing helped to dig the tunnels," he said.

Following an array of steps leading down to the depths, 10 to 12 metres below ground, we reached the main passages, which, just about adequately lit with bare bulbs, are capable of taking three to four people abreast.

Along the tunnels there are ageing pictures of Marx, Engels, Lenin and Stalin on the wall and a few feet further on are two of Mao's cultural revolution(1966-1976) slogans calling for people to dig deep, prepare provisions and oppose hegemony. There were quarters for soldiers, a hospital, cinema, arsenal, conference rooms and even a barber's shop. Various tunnels had directions pointing to Wangfujing Street, Tian'anmen Gate and even a local resident's house.

Further into the tunnel, there was water leaking from the roof but our guide explained that it was because the tunnel is relatively humid at around 78 per cent and the temperature remains at a constant 18 degrees Celsius all year around. "Elaborate ventilation systems were installed," he said as he pointed to an air-shaft that was opened to show how the ventilation could close to protect against water and chemicals. Particularly striking are the thick concrete doors, which presumably could once have sealed the passageways up from intruders or flood.

Almost at the end of this underworld you stumble upon the souvenir shop. It is just like you are wandering through an ancient lost and forgotten world when suddenly you come back to the modern commercial reality.

But it is a nice look around even if you intend to buy nothing. There is a silk factory making quilts and providing a commentary on the double cocoon silk.

I would have said that the tour was more curiosity satisfying than really fun if I hadn't left my hat somewhere in the tunnels. Back to the tunnels unaccompanied, running all the way through the trail is quite an experience close to realizing the tunnels' intended purpose. The atmosphere is quite creepy, especially when you should chance to hear the distant echoes of a tour group but no one is in sight.

By the time I fetched my hat, I was sweating which wasn't bad for a winter day with a low of minus five degrees Celsius.

How to get there: The easiest way is to take the subway to Qianmen, head for Qianmen Dajie and take the very first hutong on the left as you head south. The entrance to the underground City is at 62 Xidamochang Hutong.

Entrance: 20 yuan (US$2.50)

Hours: 8:30 am to 5 pm

(China Daily 12/30/2005 page10)