Haight-Ashbury gained its popularity in 1967 during the "Summer of Love", when an immense number of American teenagers and young people flocked to this place and experimented with an alternative way of life, establishing the Free Shop and Free Clinic and preaching love. Although this ended up as a complete catastrophe, leaving people addicted to drugs and/or homeless, the neighbourhood never lost its fame.
Today, you can come here to enjoy various vintage stores, craft beer bars, and tie-dye shirts (people actually wear and buy them here). Don't expect to experience the "good old 60s", as this place became much more touristy and commercialised, but that doesn't mean you won't feel the ambience and remnants of the culture that once resided here. You are going to encounter hippies strolling through the streets; they have never really left this place.
You will not get out of here without being offered drugs, so you might want to reconsider visiting this area with small children. There is a 7-Haight-Noriega bus route, which operates parallel to the street and connects it to Downtown. There are also two metro stops near the neighbourhood on the line N, Carl St & Stanyan St, and Duboce St/Noe St/Duboce Park.