Dumbo, which stands for 'Down Under the Manhattan Bridge Overpass,' is a neat neighborhood in Brooklyn that is at an awesome vantage point of Manhattan. There are cool rocks on the shore of Brooklyn Bridge Park that are fun to relax on and sneak alcoholic beverages.
My second-favorite outdoor-place in Manhattan. The abandoned 1.6 km rail tracks running above Chelsea down to the Meatpacking district were turned into an above-ground park. Perfectly nice place for sitting in the sun, reading, relaxing, having lunch in some green spot in the city. Nice views at the Hudson River, New Jersey, the Statue of Liberty (little small from there but still visible) and the architecture around Chelsea.