St-Valéry-sur-Somme, on the opposite side of the bay from Le Crotoy, is where William, Duke of Normandy, set sail to conquer England in 1066. With its intact medieval citadelle and brightly painted quays, St-Valéry is the jewel of the coast. The main sight is the Écomusée Picarvie, with its interesting collection of tools and artefacts relating to vanished trades and ways of life. Otherwise, activities include boat trips, cycling and guided walks, led by the Maison des Guides. Digging for shellfish is also popular, but be extremely careful about the tide: when it’s high it reaches up to the quays, but withdraws 14km at low tide, creating a dangerous current; equally, it returns very suddenly, cutting off the unwary.