U Thant Island (officially Belmont Island) is a small artificial island or islet in the borough of Manhattan in New York City. The 100-by-200-foot (30 by 60 m) island, created during the construction of the Steinway Tunnel directly underneath, is the smallest island in Manhattan. Mean sea level in the East River is sometimes measured in reference to the “Belmont Island Datum”, 2.265 feet (0.69 m) below that of Sandy Hook. read more…