Driving around one day we came across this impressive medieval structure. It can be seen for quite a distance and is clearly something a bit special and unusual. On returning home we discovered that our friends at Braye-sous-Faye had beaten us to it and written about their visit quite a while ago.
The buildings turn out to be the Chateau de Marmande. The place is near the village of Velleches in the Vienne, so not to be confused with the Cathar fortress of the same name in Lot et Garonne.
According to French Wikipedia, it is an exceptional collection of fortifications from the 12th and 17th centuries, adorning the plateau of an escarpment. The castle keep and the 40m high staircase tower were constructed to a very high quality. In addition, the chateau has a significant underground network of galleries, restored, but not open to the public.