Pollopel Island is located in the Hudson River in New York, a few miles south of the Beacon-Newburgh Bridge. It is the site of one of many Ruins of the Hudson Valley, Bannerman's Castle.
Dutch sailors traveling up the Hudson River left drunk sailors on the island to sober up. Washington Irving wrote tales of goblins that lived between Dunderberg Mountain and Pollopel Island who tormented sailors on the river.
Disclaimer: Urban exploration can be fun but dangerous. This writeup should not be taken as encouragement for unauthorized persons to visit.