To prevent the British from taking New York (again) in 1812, a fort was built here on a man-made island (since filled in with the park above). As usual, the city reinvented the space several times, as an exhibition hall, an immigration center, an aquarium and as a national monument (where people also buy tickets to the Statue of Liberty & Ellis Island). The exhibit space is basically one room with displays showing the castle’s history, plus a few placards. The rangers are very helpful and knowledgeable, but unfortunately, nobody knew of a way to get to Liberty or Ellis Islands without burning carbon.