Bannerman's Castle is an abandoned military surplus warehouse on a small island in the Hudson River, built in the style of a castle by businessman Francis Bannerman.
After the Spanish-American War Bannerman bought 90% of the US army surplus, including a large quantity of ammunition. Because his storeroom in New York City was not large enough, and to provide a safe location to store munitions he constructed Bannerman's Castle in 1901. On the side of the castle facing the eastern bank of the Hudson, Bannerman cast the legend "Bannerman's Island Arsenal".