The Grotta del Bue Marino (Sea Ox Cave) is part of a karstic system that stretches more than 70 km inland; its name derives from the nickname used by shepherds to call the monk seal, 'Su Oe 'e Mare', who used the cave to wean their pups. The cave is divided into two branches, north and south, where the encounter of fresh water with sea water is clearly visible and the resurgences create spectacular reflections, even near the mouths. The southern branch of the cave can be visited in the company of expert guides who will accompany you along a path of about 800 metres, artificially lit and crossed by a wide wooden footbridge.