The Baptistery of St John in Poitiers is claimed to be the oldest existing Christian building in France. Built in about 360 but much altered, it is worth half an hour (at least) of anybody's time.
For a plan of the building, there is a good link here, and for more information check out Wikipedia
Where are the Loire Chateaux? - The Loire River is very long and many of the administrative districts along its length make reference to it. Several French *départements* (counties) have ...