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
Old Photos of the Loire Valley - Do you ever come across old photos and wonder where they were taken? We do all the time, and very often we've been able to identify the place and find som...