The haughty Gothic jumble that is the Iglesia de Santa María de la Asunción stands out spectacularly above Castro Urdiales’ harbour. It was built in the 13th century, but additions continued until the 19th. The church shares its little headland with the town's small medieval castle, now supporting a lighthouse.
A much-reworked, single-arched, medieval bridge leads across to Castro's 500m-long breakwater.