About 30 mins or so north of Flight 93 Memorial is Altoona area. Home of Railroaders Memorial Museum (
http://www.railroadcity.com/), the world famous Horseshoe Curve (
http://www.railroadcity.com/visit/world-famous-horseshoe-curve/)
You would be in the Allegheny Portage Railroad area, home to Staple Bend Tunnel (first RR tunnel in US), the world's steepest vehicular inclined plane in Johnstown, PA (also a great flood museum).
http://en.wikipedia.org/wiki/Allegheny_Portage_RailroadOf course, there is Fort Ligonier in Ligonier, PA Old Bedford Village in Bedford, PA Amish country in Lancaster, PA
All kinds of interesting history here in PA. Depending on when you come, I may even be available to play 'Tour Guide' for some of these areas ;)
Just keep in mind, Pennsylvania is over 300 miles wide!