Re:Hwy 15 - Corning, NY to Williamsport, PA
Not too far out of your way and if not in a huge hurry, take 287 into Wellsboro. The diner is an original Sterling but has been kitchified a little for the tourists. Walk to the Penn Wells Hotel and take a look at the restored lobby. Food in the dining room is ok. There is a nice little candy shop a block down toward the courthouse. Around the corner is Native Bagel, for breakfast or lunch sandwiches and is a pleasant place to chat with the locals who frequent there.
To Williamsport, I always take 287 and/or 414 down to 220. It's really not far out of your way and gives the real flavor of the "endless mountains." 414 to 44 gets you back in the woods along Pine Creek and you have to stop at Wolfe's General Store and tackle shop in Slate Run. There is a well regarded restaurant in Cedar Run but think they are only open for dinner.