BEIJING -- Exit west from the Forbidden City, the vast tourist attraction also known as the Palace Museum for being the imperial palace in the Ming and Qing dynasties, and you cross one street before running into the walls of Zhongnanhai, the still forbidden residence compound for Communist Party leaders. Hang a right. About 50 yards up a street of classic Beijing gray stone houses is a wooden door to what was once someone's courtyard home. It's not forbidden.
It's the What Bar, and it admits anyone to its drafty confines, with a cement floor and seating so tight it's easiest to climb over someone's table to reach the squat toilet. Draft beers are $1.25, but the first one might cost more to help pay the punk band with a lead singer who falls down screaming about his death until 2 a.m. The What Bar fills up every Friday and Saturday.
''Most of the clients are foreigners. Some start in the Forbidden City, then they go out into the alleys and see us," says Qin Xuan, owner of the five-year-old bar.
The What Bar offers a first sight and first sip of what Beijing morphs into every night after 7 or 8. Ten years ago, tourists had to rely on hotel restaurants for a drink after sightseeing. Now, half a mile north of the Forbidden City in the Houhai bar district, night life gets thick enough to trap bar hoppers in an outdoor pedestrian mob.
Although this new entertainment industry has expanded mostly on demand from well-to-do Chinese youth looking for ways to cut loose, night life now earns chapters in tour guides and its own section in local foreign-language entertainment magazines. It welcomes foreign faces looking for something small, smoky, loud, and cheap.
''The night life is definitely accessible and moderately friendly," says Jim Boyce, a Beijing resident who writes a night life newsletter. ''It's grungier, maybe earthy is a more politically correct word, with lots of underground music and student bars," he says, comparing Beijing to other Asian cities. ''Even a place like The Tree [Belgian beer and pizza], which draws a lot of moneyed expatriates, is grungy, not that there's anything wrong with that."
The Tree. The Loft. The Den. Say Yes Bar. No Name Bar. These Beijing spots and their countless competitors have coalesced into 10 districts of 10 to more than 100 places apiece. Usually just one or two rooms, the bars occupy the ground floors of housing blocks, high-rises, and converted courtyard homes.
Flank to flank with the bars, mutton kebob stalls open until past 2 a.m. belch charcoal smoke that overwhelms the fresh-ground scents of neighborhood coffeehouses.
''Ten years ago, no districts, just the few-and-far-between bars," recalls Michael Wester, formerly of Newton and now general manager of the monthly magazine That's Beijing. ''Five years ago, the age of the district, Sanlitun and Wudaokou the only games in town," he says, naming the city's first two consolidated night life regions.
''Now, district diversification and diffusion," Wester says. ''Now there appear to be bars in many places and a blossoming of multiple-bar areas, and no longer is it necessary for you to be in a district to survive."
Much of the night life is concentrated where travelers would go anyway. Houhai, a district named after a lake surrounded by night life, sits at the north end of a conventional tourist axis that starts from Tiananmen Square, moving through the Forbidden City, then Jingshan Park, known for its panoramic views, and Beihai Park, known for its garden paths. The historic bell and drum towers are just north of Houhai.
Sanlitun adjoins the Yashou Clothing Market, which is known for bargains, and because it's considered Beijing's original bar district, has become a tour destination itself.
Sanlitun ''is in guidebooks, and also always in the monthly free mags, so quite high profile," said Alex Pearson, owner of The Bookworm, a bar, cafe, and library in the village-like district. ''There are the coach loads that are taken just to Yashou shopping plaza. The backpackers see Poachers [a pub known for 60-cent beers] and the back streets."
A 20-minute taxi ride from the new summer palace or a 20-minute walk from the old palace ruins leads to Wudaokou, a district where literati coffeehouses dominate. A visit to the embassy district around Silk Alley and the Friendship Store might end with dinner and drinks at one of five Russian restaurants, the white-collar Centro bar at the Kerry Center Hotel, or the Chinese-style Peace Teahouse outside Temple of the Sun Park.
Because taxi fares range from $1.50 to $5 and Beijing has little street crime except for the occasional pickpocket, revelers can float easily around the city until sunup.
''You cannot really compare the bar culture in Beijing to that of many other countries, as many others have had some sort of culture in place for 10 to 20 years, if not longer," says Gregory Dover, owner of Bar Blu, a Sanlitun dance hall with blue floor lights in the seating area and a predominantly foreign clientele.
''The culture is building, however, and I don't think it will be too long before we can compare to other countries," Dover says. ''I have never felt as safe as I do in Beijing. On top of that, it is a very easy city to get around in."
Among bars heretofore dependent on a regular clientele, a race is on to stand out in order to lure tourists.
Although grunge is still the standard, enterprising owners are scaling up with pianists, mosh pits, or imported wines. Other businesspeople try for niche markets with gay bars or hip-hop clubs.
Standouts include not only individual establishments, but also entire districts. One is the proudly quiet strip of tree-shaded bars and cafes on Weigongcun Road outside the Beijing Institute of Technology. Another is Factory 798, which houses at least 20 public art galleries and half as many eat-and-drink places open by night in a cavernous former Eastern European-style munitions plant.
Popularity is also putting stress on bigger bar districts. Crowding at Sanlitun and Houhai raises noise and cigarette smoke levels indoors while drawing beggars and touts in pursuit of foreign money to clog curbsides. Drugs pervade some bars, and vendors of pirated CDs work tables at others.
Traffic can be choked, especially on the single-lane alleys of Houhai or Sanlitun, and local authorities seldom intervene.
''Sorry, gone" is another common Beijing discovery. Demolition of Beijing's traditional brick and stone low-rises for redevelopment (and, remember, the Olympic Games are coming in 2008) can put a bar tenant out of business in one night, rendering useless the advice in guides and even the latest magazines.
The Bookworm started alerting customers of its new address two months ahead of demolition, but lost a few ''stragglers," Pearson says. What Bar picked its Forbidden City site because it's not likely to be demolished.
Lack of an institutional bar culture further hurts business. Bar owners often are hobbyists, rather than businesspeople who have researched what customers want. Some invite so many friends in that customers often feel they are crashing a private party. The waitstaff may be surprised to see non-Asian faces or unqualified to discuss their liquor selection with authority. Most bars offer common bottled drinks rather than draft beer or expertly mixed drinks.
To maximize headcounts, bars also may place chairs or stools so close to one another that pushing back to get up causes someone else to spill a drink. Restrooms can be outside and 50 or 100 yards down a frozen and unlighted alley.
''The level of service is the biggest issue that is slowing down the industry," Siegel says.
Earthy What Bar is so full of foreigners there are plans to expand it. What Bar II, at about 1,000 square feet, helps anchor the infant Yuan Dynasty bar district, also known as Dadu Street, near the University of International Business and Economics. Chinese bar hoppers have found it, and a promo for the district is running in That's Beijing.
Foreigners, happily enough, have plenty to choose from already.
Contact Ralph Jennings, a freelance writer in Beijing, at thefrozennorth@yahoo.com. 
