I can think of many worthy candidates, but the tour which my brain is selecting at this moment in time was in SW France, up the Dordogne & Lot valleys from Bordeaux, then south toward Toulouse. The region has a great network of quiet secondary roads with little traffic, combined with gorgeous scenery full of castles, gorges, & medieval villages. There are numerous caves which can be visited, too. Add some of the best food in all of France and it's close to touring perfection. On the particular tour I'm thinking of, we had absolutely perfect weather, as well.