Social Workout

Hello! I'm alive! lol. Finished one month of Insanity....didn't really start the second month :( My internet has been down all this time, but know we're back in action! Yesterday I did 6 intervals of sprinting (30 seconds sprinting, followed by 90 second low intensity) I want to do this twice a week.
Does anyone know of real running tracks in Manhattan? I went to Riverside park yesterday and I couldn't find it. The nyc.gov site said that it was on 73rd and riverside, but that wasn't the case... I really want to avoid running on concrete. PLEASE HELP. At least maybe some grass or dirt trails I can follow.,,,?