So. You’re stuck playing tour guide for a few hours? Have no fear: Big Onion Walking Tours won’t merely kill time and impress your guests. Even the most jaded New Yorker will pick up a fact or two during a comprehensive and fascinating two-hour walkabout. Tours run on a shifting schedule every day except Thanksgiving, year-round; choose from a variety of subjects, including a Brooklyn Bridge and Heights walk, a multiethnic eating tour, the “official” Gangs of New York tour, Central Park walks, and on and on. Most cost $20 for adults and $15 for students and seniors (excursions involving food or museums will run ya more). The tours, which began in 1991, are led by educators and graduate students who really know their stuff. Don’t be afraid to come prepared with questions!