the beaches around Sables d'Olonne are great and stay nice into the autumn.
Ile de Re is a world heritage site with a massive 17th century fortress on it, nice beaches, ice cream and salt marshes.
La Rochelle is a beautiful old city, really chilled and cozy, great waterfront, historic centre and aquarium.
Saint-Nazaire is the site of the most daring special operations raid of ww2.
Bordeaux and the Gironde estuary has some of the best wine in the world.
Overall it's a pretty blessed part of France, the only downside is that being on the Atlantic means it gets storms in the winter and the summer temps are lower than most of France, but still nice.