June Trip- VA/D.C. Area

My father-in-law has an upcoming H.S. Reunion, which will be in Virginia, in June. This will be the last one that he attends, so he says, because he's 76 years old and he's ready to be done with them. I guess. lol. He's a retired Marine Colonel who is also a pilot and he refuses to travel by way of commercial planes. So, Devil and I are at his house a few months ago and he gives us an entire story, much like I have, and then says, but if you and Angel will drive us, then I can attend my reunion for the last time! Of course we were caught off guard but how could we say "no" to that? I mean, he had his story rehearsed and polished up so that we were on the edge of our seats waiting for what was next. We just hadn't counted on the- "unless you and Angel drive us, we won't be able to attend" part. lol. Anyway, we plan on spending 3 days in his small home town, which he says is one day too long as it is, and then we're heading up to the D.C area and over to Philly from there. I'm asking for suggestions on places to visit and sites to see, so please comment and let me know what you think I should make time for. Keep in mind my father-n-law and his wife will be in tow. 
It appears that all of June will be spent on the road. The first half of the month we'll be in Seattle moving Devil's sister back to Austin. We'll be home long enough to do laundry and feed the dogs. I sure hope June is good to me. lol.