I visited an abandoned castle on a New York island that's only accessible by boat. It was hauntingly beautiful.

The abandoned Bannerman Castle is deteriorating on the Hudson River in New York. The island it sits on opened to visitors in 2020. National Archives and Records Administration, Joey Hadden/Business Insider

Sitting on Pollepel Island in New York's Hudson River , a stunning piece of history is slowly crumbling away.

Bannerman Castle was built in the early 20th century as a fortress for weapons by Scottish arms trader Francis Bannerman, The New York Times reported. Gunpowder exploded inside the castle in 1920, and it was abandoned about 30 years later.

Then, in the early 1990s, the Bannerman Castle Trust led efforts to restore the structure and make the island safe for public visitation . It's been accessible since 2004 and open for tours since 2020.

I got a private tour of the island in 2019 — before tours were available to the public.…