I don't know how out of the way this place is from your route, but my favorite place in France is Connelles. It's a hilly village less than 2 hours north of Paris. Richard the Lion heart's castle ruins and the famous Sherwood forest (from robin hood tale) are all a short distance away with amazing views. Chateaus and castles are found among the hills. Its really quite picturesque.
Actually almost nobody in France knows the village of Connelles. We all know the castle of Richard the Lionheart "Château-Gaillard", close to the small town "Les Andelys". Lovely place in Normandy with a great view of the river Seine. North West of Paris.
I also had to check whether we were talking about the same castle.