Pollepel Island is an island

Island

An island or isle is any piece of sub-continental land that is surrounded by water. Very small islands such as emergent land features on atolls can be called islets, cays or keys. An island in a river or lake may be called an eyot , or holm...

 in the Hudson River

Hudson River

The Hudson is a river that flows from north to south through eastern New York. The highest official source is at Lake Tear of the Clouds, on the slopes of Mount Marcy in the Adirondack Mountains. The river itself officially begins in Henderson Lake in Newcomb, New York...

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Also known as Pollopel Island, Pollopel's Island, and Bannerman Island, it is the site of Bannerman's Castle
Pollepel Island is about 50 miles (80 km) north of New York City

New York City

New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...

 and about 1,000 feet (300 m) from the Hudson River's eastern shore. It contains about 6.5 acres (26,304.6 m²) — most of it rock.

The principal feature on the island is Bannerman's Castle, an abandoned military surplus

Military surplus

Military surplus are goods, usually matériel, that are sold or otherwise disposed of when no longer needed by the military. Entrepreneurs often buy these goods and resell them at surplus stores. Military surplus rarely includes weapons or munitions, though they are occasionally found in such stores...

 warehouse.