Completed in 1811, Castle Williams on Governors Island in New York Harbor was a cutting-edge coastal fortification designed by Lt. Col. Jonathan Williams. As a key part of the Second American System of coastal defense, it protected New York's inner harbor alongside Fort Jay, Castle Clinton, and others. In the 1830s, its military role diminished, leading to its use as barracks and later a prison through the Civil War and early 20th century. Despite plans for demolition in the 1960s, Castle Williams was preserved and repurposed as a community center before becoming part of the Governors Island National Monument. Listed in the National Register of Historic Places in 1972, it was restored by the National Park Service in the mid-1990s. You can visit this historic fort today to learn about local history and take in the views of the city skyline.