Going to this island on the East river was my perfect plan for a Sunday afternoon. You can either take a bus, the train or my favorite option: the tramway. It is only a 5 minites ride from East Midtown with a great service, there is one tram following the other and, something important to remark, once you have your Metrocard you can use it as with any other public transportation; no need to pay extra money!.
I feel this is another way to experience Ny from the sky. You get into this cars, go over the streets through the buildings, cross the river and get off at a peaceful island which has little relation with Manhattan and its atmosphere. Roosevelt is a quiet place where you can actually enjoy the landscape and the amazing views of New York. Surrounded by history and nature this is another oasis in the city where you can just relax and walk around.