18. Fort Tilden

New York City’s only 20th-century fort is Fort Tilden, located in the Rockaways. After serving as a  coastal artillery installation, the fort went on to house Nike missiles. It is currently run by the National Park Service and is open to the public.

To learn more, read our past coverage of Fort Tilden and our Urban Exploration of the Abandoned Fort Totten. Curious about nautical architecture? Check out our roundup here.

Next, read about the Top 10 Secrets of Grand Central Terminal.