Enjoy one of the largest collections of art in the US and enjoy a run (or slow walk) up the famous Rocky steps. Take a walk down the Benjamin Franklin Parkway to see city hall with the famed William Penn statue atop.
Steven Starr is a renowned restauranteur credited with reviving Philadelphia's food scene some 30 years ago. He has numerous restaurants throughout the city and all are great. Check out Morimoto for some cool sushi eats or El Vez for some fun tacos in a happening part of town.
If you want to do a little shopping, consider checking out Rittenhouse square, which is one of the ritzier parts of Philly. Cute shops (both small and large) can be found on Walnut street between 19th and Broad st. For those wanting to get lost in a mall, check out King of Prussia, one of the largest malls in America and 30 minutes outside of Philly.
If your a history nut, there is no better place than Philly. Philly has lots of historical monuments and museums related to the revolutionary war period. Check out the Liberty Bell (and its crack). Across the street you can find Independence Hall where the Declaration of Independence was signed.