11. Castle Clinton/Battery Park
Castle Clinton was originally situated off the coast of Manhattan. However, as a result of landfill, it is now fully surrounded by land and sits in Battery Park. It was constructed between 1808 and 1811. After being decommissioned, the fort was used as the country’s first immigration center, a theater, and an aquarium before almost being demolished by Robert Moses. It was designated a National Monument in the 1940s and is currently run by the National Park Service.