The great cave of La Cuevona de Ribadesella, in Asturias, and its beautiful natural surroundings: https://www.outono.net/elentir/2025/02/28/the-great-cave-of-la-cuevona-de-ribadesella-in-asturias-and-its-beautiful-natural-surroundings/ A video by Aventuras Entresierras shows the incredible places in that area.