Bannerman Castle is located on Pollepel Island in the Hudson River across from Fishkill, NY.  The “castle” was a storage building for surplus ammunition, uniforms, and the like until sold, which was the business of the Bannermans.  The island contains more than just the “castle” — it was also the summer residence of the Bannermans.  The island is now part of the Hudson Highlands State Park.  “Hard hat” tours are run on the island, including a boat ride out to the island.

Link: About Bannerman Castle