Explore the lighthouses of the Gironde
Start out from Montalivet in the morning (bring a picnic and some warm clothing) and head off to the Phare de Richard situated near the village of Jau-Dignac-et-Loirac on the Gironde Estuary. (about 30mins drive from Montalivet) In July and August the lighthouse is open for visits from 11h- 19h and takes about 30 mins for the visit.
Then its a half hour drive up to Verdon-sur-Mer to find the next lighthouse called Saint-Nicolas ( I'll let you unearth this 12m lighthouse).
Across to the Phare de Grave at the Point de Medoc (10 mins drive) open from 11h to 19h, before the highlight of the trail the Phare de Cordouan, which involves taking a boat leaving from Port Bloc ( next to the ferry crossing) so your visiting time will depend on the tides and takes about 4hrs for the round trip.
Information here for the timetables: www.phare-de-cordouan.fr