I can certainly recommend the local Zoo from personal experience. You might want to take your car on the ferry across the mouth of the river Gironde and do some vineyard visiting and wine tasting!

You might also visit Bordeaux, Arcachon (suggest taking the train to avoid the Bordeaux ring road) and visit the massive sand dune Le Pyla. Going northwards, you could visit Futuroscope (I'd plan a cheap overnight nearby say in a Formule 1 hotel). The Donjon (castle with dungeons) in Niort is worth exploring, also a trip on a flat bottomed boat in the Marais Poitevin - persuade your boatman to put his lighter to the water and show you the methane burning off . You could also enjoy a trip to beautiful La Rochelle and its superb aquarium at Les Minimes where you walk around surrounded by sharks and other fish;

Otherwise chill and relax ... but drink plenty of water and wear plenty of sunscreen as it gets VERY hot in this area in Summer! Have a great time.