Go to Central Park, New York.
I visited NYC on summer 2013. I rent a bike to go through the whole park, I went around the park twice. This is one of the reasons why I love New York and I would love to do it again if I come back to NY.
rent a bike! picnic would be nice. don't forget to bring a hat or water bottle if you go to central park on summer. if you like to run/jog, this is the best place to exercise. bring a camera!