Although close, La Baule is not Brittany and has very little of a Breton character. Often called the 21st arrondissement of Paris (a nickname also applied to Deauville in Normandie) because so many affluent Parisians have second homes there. As a favourite “station balnéaire” for principally French visitors, it does empty out pretty quickly once “les vacances” are over on the last weekend of August or, sometimes, the first weekend of September. I have never been out of season so not quite sure what you should expect in September.
I’m a huge fan of La Mare aux Oiseaux in Saint-Joachim in the very atmospheric Brière marshes (also a pocket of Breton speakers or so I am told), about a 30-minute drive from La Baule.
I have an auntie who, like half of Paris 16, summers in La Baule, and a meal at La Mare aux Oiseaux is one of my favourite rituals every time I go to visit her for a long weekend. Excellent modern Breton/ “locavore” cuisine. Setting with lots of personality. I haven’t been yet this year but usually a very welcoming young team who add significantly to the enjoyment. And because of the location and cuisine, a rather unique experience. https://mareauxoiseaux.fr/fr/restaurant-eric-guerin.html
For seafood, I’ve always had very enjoyable meals at L’Océan on the Atlantic side of Le Croisic…. fab terrace overlooking, surprise surprise, the ocean, and very good fish-based cuisine. In La Baule itself, Le Billot on place du Marché/ avenue des Petrels across from the “marché central”/ daily covered market is a great place for oysters even if the rest of the menu is not particularly fish-y—and a more down-to-earth vibe and clientele compared to many other restaurants in La Baule.
And speaking of the marché central it’s a great place to find local specialties like fondant baulois, craquant guérandais, gâteau nantais, wonderfully affordable fleur de sel de Guérande, and caramel salé as well as the original pie-size version of kouign amann. I also like the covered market in neighbouring Le Pouliguen and the little shops (touristy but surprisingly good quality) in the nearby walled town of Guérande.
Beach life is obviously well developed. There are a lot of beach front restaurants, some rather chic and obscenely overpriced. I usually end up at Gulf Stream Club because my auntie is a member. Typical of beach restos, a rather one-size-fits-all menu but good enough for a very enjoyable lunch on the beach and a better price/quality than most other beach restos.
For an immersion in Breton life (and history), I always make time for a side trip to Vannes, an hour’s drive north of La Baule. Ultra-picturesque, photogenic, historic town notable for its cluster of very good restaurants. I had an excellent lunch last year at L’Empreinte (which I found thanks to lefooding.com) in the very atmospheric and historic old town (largely medieval and très breton) of Vannes… very short menu but everything of excellent quality and the service was outstandingly personable. My auntie also suggests La Chaumière de Pomper, a rather upmarket crêperie in a rural setting between Vannes and Baden, for a sample of something more folklorique (hint: “chaumière” means thatched house/ cottage).