Beach approachable by public transportation and can be connected with a visit of MOMA PS1 Art Installation (Katharina Grosse House) Also less crowed than other beaches in NYC.
My friends, Dee & Ricky, recently opened up their own restaurant at the ripe age of 24 in the Clinton Hill neighborhood. I stop in here every now and then for the roti. Also, there's a really cool (Nigeria-owned) sandwich & smoothie spot next door that is not pictured.
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.