Beach where you can take your dog in Castro Urdiales, Cantabria, according to official gazette.
«Los perros podrán acceder, circular y bañarse sin correa a excepción de los meses de Mayo a Septiembre ambos incluidos»
Animal Ownership and Protection Bylaw (Ordenanza de Tenencia y Protección de los Animales, art. 16.a); the town council may set other periods of prohibition. 2024 press reports mention a ban from 1 May to 1 October.
Source: Official gazette · 2018. Rules change every season: check them before you go.