WNYC Transmitter Park offers a nice contrast to the hustle and bustle of downtown. Meander around the grounds or fling off your shoes and feel the soft grass under your feet.
You'll be spoiled for sightseeing choice when in Greenpoint. WNYC Transmitter Park is a good place to start here, but there are many other worthy sights to consider. Times Square, Statue of Liberty, and Broadway are not far from the recreation and green space and will top off your day nicely.