Liberty Bell, Independence Hall, National Constitution Center, Betsy Ross House, Museum of the American Revolution, Valley Forge National Historical Park
Princeton University, Nassau St., The Bent Spoon, Princeton Battlefield State Park & Princeton Cemetery (legible gravestones date back to 1760, including Aaron Burr, President Grover Cleveland, John Witherspoon, Paul Tulane, and others)
Built between 1908-1912, Fonthill Castle is made of reinforced concrete and served as the home of archaeologist, anthropologist, ceramist, scholar and antiquarian Henry Chapman Mercer (1856-1930). Mercer built Fonthill Castle as his home and as a showplace for his renowned, hand-crafted ceramic tiles, and international collection of tiles. (Allot 1 hour)
While visiting Fonthill, consider visiting Mercer Museum. The Mercer Museum is a six-story reinforced concrete castle designed by Henry Mercer (1856-1930) and completed in 1916. The museum features a core museum collection of over 17,000 pre-Industrial tools. This permanent collection offers visitors a unique window into pre-Industrial America through sixty different crafts and trades, and is one of the world’s most comprehensive portraits of pre-Industrial American material culture. Oh yeah, and many of the artifacts are uniquely suspended around and above you. (Allot 2 hours)
Consider taking the Staten Ferry. It is the closest you can get to the Statue of Liberty for free.