Fort Montgomery sits on an island in New York, a the conjunction of Lake Champlain and the Richlieu River, withion spittin' distance of Canada. The three-story stone building, built over several decades including the Civil War era. It was decommissioned gradually around the turn of the 20th century, and was sold to a private owner in 1926. What was the purpose of Fort Momntgomery? To defend the US from Canada, of course.
The fort has the kind of wacky pedigree that might tantalize a history buff buyer. A previous fort built in 1816 on the same site was enough to launch a thousand face-palms: Because the engineers were a little murky on exactly where the border fell, a precursor meant to fortify the U.S. against northern invasion accidentally went up on the Canadian side. As James Millard, a historian who literally wrote the book on the moldering remains, has noted, that structure earned the nickname Fort Blunder. The highly visible, expensive mistake was eventually abandoned and plundered. Then, when the international border was redrawn in the 1840s, positioning the island in U.S. waters, Fort Montgomery went up in the footprint of the folly.
Fort Montgomery has been on the market since the 1980s, and the price has dropped from nine million in 2006 to one million dollars today. The building is in poor shape, but it's on the historical register. Read more about this unique real estate opportunity at Atlas Obscura.
(Image credit: Mfwills)