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
Day Tours for Groups - We specialise in customised private tours of the Touraine Loire Valley for small groups. Our typical clients for a day tour are couples, but we can take mo...