Sometime around 1973, concerts started taking place at the South Street Seaport at what looks like Pier 17 (which still houses concerts today). The caption on this photo—which was taken in June of 1973—reads, "Folk singing and dancing has found a new home at the South Street Seaport on the East River near Brooklyn Bridge. Enthusiastic crowds gather several times a week during the summer to enjoy the show and the music, view the harbor boats, and breathe the sea air."
Recently we looked at how New York's music festivals have been struggling over the past few years—but even these days good crowds turn out on a weekly basis to the Seaport for free, live music. It is near a lot of subway lines, after all.