I stayed a couple of years ago near Philladelphia and I've always wanted to come back. I really like the northeast cities as you can see modern skyscappers and and small old houses charged of history. Philly is definitely one of them. Our first stop was of course the Liberty Bell and Independance Hall. This is the place where the United States were founded. When visiting Independance Hall you are immegered in that time period and feels like you were there. (http://www.nps.gov/inde/index.htm)
While being in US history, you can stop by Betsy Ross' house. She is thought to be the one that sewed the first US flag. (http://www.historicphiladelphia.org/betsy-ross-house/what-to-see/)
A little further you can visit the place where house of Benjamin Franklin used to stand. (http://www.benjaminfranklinhouse.org/site/sections/about_house/default.htm)
To finish our historic tour we walk to the Elfreth Alley (http://www.elfrethsalley.org/). This old street seems to come from another time. We you look around you see large roads and tall buildings but when you are in this narrow street you're back in time and can almost imagine the horses and carriages running aound.
Of course Philadelphia is not only for its history. You have to try the Philly cheesesteak at Jim's (http://www.jimssteaks.com/SouthStreet.html) or a soft pretzle.