San Francisco's Chinatown is the largest outside China (sorry, NYC) and is the oldest in North America. Chinatown began with two Chinese immigrants in 1848 and has grown ever since despite immigration laws, harsh exclusion acts, and general racism. Though it has become a tourist destination, San Francisco's Chinatown still maintains its historical traditions and culture. Chinatown has its own government, hospitals, social centers, churches, and schools. Though it is only 1 by 1 1/2 miles in area, Chinatown has an estimated 110,000 residents - making it the most densely populated neighborhood in San Francisco. Its population grew so much in the later 20th century that other mini-Chinatowns have been established in The Richmond, The Sunset, and Visitacion Valley.
Besides getting some authentic Chinese food and shopping for unauthentic designer items, another popular "thing to do" in Chinatown is to visit the Golden Gate Fortune Cookie Factory.