Under the vaulted ceiling of Notre-Dame de Bon-Port in Les Sables-d"Olonne, a seaside town in western France, the stone ribs still guide the gaze upward. Construction of the soaring vaults began in 1646. The church—officially recognised as a French historic monument since 1993—stands on the site of a 13th-century chapel, a reminder of deep-rooted spiritual life on the Atlantic coast.