This is one of the Governors Island Caches. You will need to take a ferry to get here; the Island is open late May to late September, seven days a week. This will provide a beautiful view of New York Harbor and the Statue of Liberty.
You can only reach it by walking or bicycling. This is a micro cache near a very old structure. Bring a picnic to this point of the Island. Be very very wary of Muggle when making the grab. Be sure to take a selfie with the Statue of Liberty behind you, the view is that good.