Welcome aboard the RoadTrip America Forums!

Pittsburgh to Philadelphia is a good 5+ hours under the best of conditions without any stops, so there's not a lot of time for wandering off the Turnpike, but still I can think of one worthwhile 'detour' and a couple of stops you might enjoy. At Breezewood, leave the Turnpike and take I-70 (south)east into Maryland and visit Fort Frederick in Big Pool and then take MD-66 north/MD-77 east through Catoctin Mountain National Park (Camp David) to US-15 north up to Gettysburg. Even an hour spent walking those grounds would be worthwhile. US-15 north from Gettysburg would put you back on the Turnpike at Harrisburg.

AZBuck