La Rochelle, capital of Charente-Maritime and one of the most livable cities in France, is a pretty good place to go and get nautical. Go for a wander around La Ville Blanche (as La Rochelle is known) and get some great views by climbing the two towers that used to protect the harbour from the troublesome English. A highlight is visiting La Tour de la Lanterne, which has acted as a lighthouse and a prison and has graffiti made by forlorn English prisoners in the 18th century and a backgammon board carved into the floor by someone in room 4. You could also visit the aquarium, check out the maritime museum or head to town's long sandy beach before indulging in some local seafood.
Eric Pouhier, CC BY-SA 2.5 , via Wikimedia Commons