Both grottos are of great beauty and interest, not only for geologists, speleologists, historians and palaeontologists, but also for the common visitor.The grotto of the Bue Marino (once a shelter for the very rare monk seal) is situated in the Orosei gulf and has two independent entryways: one from inland and one from the sea. The grotto extends for over 4 km, considering also all of the various underground tunnels that characterize this area in the Dorgali territory. It also presents, as the grotto of Ispinigoli, numerous concretions and many carsic effects. In the grotto of Ispinigoli there is what seems to be the longest stalactite in Europe: 38 meters