While there, soak in Historic Philadelphia, walk through some of the very buildings that our Founding Fathers shaped this nation. If you make it here in the fall, a trip along Delaware Rivers scenic roads to watch the leaves change is fantastic...theres many craft breweries in the area as well
While I haven't had the chance to come across such nice vistas like Krutj, and the Liberty Bell has never interested me enough to go see it; there is one thing I can recommend: beer. The Philadelphia area has a very vibrant microbrewing community, and you can find great pubs, bars and restaurants in Philly that serve great locally brewed beer. I think Pennsylvania beer will give any state a good run for its money.
Other than that... well, there's the Philly murals, and the ever popular Rocky statue (*sigh*), and as already mentioned, Amish country is a nice and unusual thing to see.
Like some people have mentioned, Philadelphia is unique. Obsessed with their sports; their sense of humor is weird and awesome, just like Always Sunny in Philadelphia... its an awesome place.
Yuengling Lager, Lebanon bologna, Hershey chocolate, Rausch creek, Gettysburg, Amish people, Philly cheesesteaks (although I don't think Pat's or Geno's are any good) are all good reasons to visit. If you are into the outdoors you'll find plenty to do.