I did stay also in Saint-Martin-de-Ré on the Ile-de-Ré for a while this summer. It was lovely to do not too much in such a beautiful place. It's a World Heritage Site, and completely enclosed by really interesting Vauban fortifications. Most days I went for long walks along the ramparts. I drew and took pictures of buildings, I read a little and swam in the pool in the garden. In the way of old postcards I should put a cross on my bedroom window, but it's the one that's open in the photo above.
These images show the fortifications, today, and as they were laid out in the late seventeenth century. The citadelle is still a prison. Curiously, the guide book advised that only one prisoner had escaped recently. In his bid for freedom he had stolen an inflatable dinghy from a tourist and attempted to paddle across to the mainland, but he had been "caught very quickly".