I'm really into history and all that, so Philly is like a big giant play ground to me lol.
There's Independance Hall, Ben Franklin's house, you could take a horse and buggy ride around the city, you can go to the Mint to see how they make money (really cool actually), you can visit Franklin's grave. I'm not sure if its open to the public or just groups but you can go in Betsy Ross's house. That was a lot of fun! hmmm, there's lots of stuff to do!