The zoo isn't a museum per se , but it is a Washington institution that generally shuts its gates by 6 p.m., making the annual after-hours event Brew at the Zoo an all the more coveted ticket. This year, 38 microbrewers will serve samples while the Batala women's drum troupe and rock band Gonzo's Nose play to an audience made up almost exclusively of 20- and 30-somethings (the event is 21 and older). You can't actually roam the zoo with your beer. The event is confined to the animal-bereft path between Lemur Island and Kids' Farm. With the $50 general admission ticket, visitors get a keepsake mug for beer samples measuring about two ounces; spring for the $85 VIP ticket, and brewers will pour you full glasses. (Tickets for nondrinkers are $15.) Vendors sell barbecue and pizza, but hors d'oeuvres are provided with VIP tickets. The event attracts 2,000 people annually and is perennially sold out, so get tickets in advance. Brew at the Zoo is 6-9 Aug. 20. Drinks: Included in admission. Attire: Casual. (The tents are in the grass, ladies, so leave the heels at home.) National Zoo, 3001 Connecticut Ave. NW. For tickets, call Ticketmaster (202-397-7328) or avoid service fees by getting tickets at the visitor center front desk, open 10-5. Information: www.fonz.org/brew.htm. 