Cayeux-sur-Mer is a shingle town. The beach is pebbles rather than sand — the same flint shingle that gets dredged along this coast — and the answer to walking on it is les planches, a boardwalk that runs for three kilometres behind more than four hundred beach huts, each painted a different colour and each individually named. It is the longest promenade of its kind in Europe and the single most photographed thing in the bay.
The town proper is quiet, low and a little weather-beaten, with a lighthouse at Brighton — a hamlet at the southern end named, optimistically, after the English resort. The real draw is at the other end: the Pointe du Hourdel, a spit of shingle four kilometres north where the Somme meets the sea and where the largest colony of harbour seals in France hauls out on the sandbanks at low tide. Several hundred animals are usually visible through binoculars from the shore, and guided walks go out from the hamlet when the tide allows.
Saint-Valéry-sur-Somme is 15 km round the bay, and the heritage steam railway connects the two in season.