I used to live in Atlantic City, and we would do trips to Philly pretty often.
There is lots of American history there if you like that sort of thing. Independence Hall, the homes of Ben Franklin and Betsy Ross - that sort of thing. Lots of historical markers that you can read while walking around the historic district. Probably too cold for that, though. You can also visit the mint there and watch them make money, which is kinda cool. Its indoors.
We also like to go to South Street where there are lots of restaurants, bars and interesting shops. Don't know if you want to take a nun there though.
Do you have AAA? If you go on their website, you can search and narrow down by your interests. They also list hours, admission fees, etc.
Have fun!!