The eastern part of PA is unfortunately heavily popluated and trafficked.
Ricketts Glen State Park in PA (along Rt. 487- see below)- 21 waterfalls in a 3 mile hike, and there is camping.
Just 32 miles south of the park on Rt. 487, in Bloomsburg on Rt. 11, is Bills Custom Cycles, with a neat motorcycle museum of sorts (Bills Old Bike Barn), and it's on the way to Lancaster. Routes 339 or 125 are both the best north of the Lancaster area.
Depending on where you enter PA from the north, the best north to south ride in the eastern part of the state:
Rt. 154 from Canton, south to Rt. 220, (154 is one of the better bike roads in PA) In Forksville, turn R. over the covered bridge to eat at a restaurant set in the middle of a country store (not a tourist trap but an actual local place), Rt. 220 S. to Rt. 42s, Rt. 42S to Rt. 487S, to Rt. 61 east into Shamokin (passing coal mines and coal mining towns (think Molley McQuires as you look at the tiny houses in tight rows which used to be coal miners houses), to Rt. 125 S (R at the Dunkin Doughnuts in Shamokin). If you take 125 (the best road around there), go straight at Good Spring toward Joliet instead of staying on 125, and then go straight accross Rt. 209 toward Ravine, which will bring you back to Rt. 125, but traveling on twistier roads. Go straight at the light, through Pine Grove, turn L onto Rt 645S, to Rt. 422. Turn left and go 1/4 mile to Rt. 501 S, to Rt 897S, to Rt. 30. (Rt. 501 also goes from Pine Grove to Rt. 422, but is heavily trafficked, and not as twisty) You will be passing horses and buggies from 645 on. You can turn west on Rts 23 or 340 to get to Lancaster instead of going all the way to 30. The Strasburg Railroad museum is not bad. Gettysburg is interesting, ((south west of Lancaster) although I haven't actually been there since the early 80s.
Another great north to south route, almost in the direct center of PA, is 144 south, starting from Galeton on Rt. 6, to 26 south, into Maryland and then WV.
Along Rt. 125, turn R onto Rt. 25 and go a few miles to the Midway grocery and gas station- they have the best fried chicken plus other food and you can sit on the back porch and eat looking at good scenery.
The Shady Maple Buffett, on Rt. 897 by the Rt. 23 intersection is locally famous for it's PA Dutch style food.