That would be U Thant Island (officially known as Belmont Island), a rocky spit of land just south of Roosevelt Island in the East River. It ranks as the tiniest of New York City’s dozens of little islets.
Doesn’t look like a bad place to catch some sun, right? Unfortunately, people aren’t allowed there. This half-acre is maintained by the parks department as a bird sanctuary.
So what’s with the odd and unofficial name? Originally called Man ‘O War reef, it was created with landfill from trolley tunnels dug under the East River. Augustus Belmont Jr., of Belmont Park and subway financier fame, completed the job and got naming rights.
In the 1970s, mostly forgotten, it was unofficially renamed U Thant Island (after the former U.N. Secretary General from Burma) by a group of U.N. employees who followed a mystic in Queens.