This extensive cave system full of stalactites and stalagmites, and a lead and zinc mine before 1979, makes for a popular outing inland from San Vicente de la Barquera. The one-hour visit goes 400m into the cave in a mine train then continues on foot. Booking ahead is highly recommended. A separate adventure tour travelling 3km in (€32, 2½ hours) opens up an extraordinary subterranean world. It's about 30km southwest of San Vicente: turn east off the CA181 at Rábago and climb 7km.
