If you're looking for a relaxing weekend trip in France, make sure to consider this hike on the "Côte d'Opale" from Boulogne-sur-mer to Calais. It's surely one of the most beautiful trails of the coast. Neverending views on the sea, little towns, sand beaches, and not much elevation gain.
It takes 2 or 3 days to walk the 50km of this hike, depending on your walking pace and shape. You will need to plan ahead and find a place to sleep between the villages.
Even though this trail takes more than a day to finish, you can try walking only a part of it, and visiting the coast by car, train or bus.