A marvel of early-20th-century engineering, Porto Flavia is a port dug into cliffs 50m above the sea. Consisting of two 600m tunnels and an ingenious mechanical arm, it was used to load zinc and lead ore directly onto cargo ships waiting in the waters below. To find it, head towards Masua's beach from where a road leads back uphill and around the coast for about 2.5km. Visits are by guided tour only; it's best to book through the tourist office in Iglesias.
Built in 1924, Porto Flavia revolutionised the system of shipping minerals from Masua. Before it was built, the mined ore had to be loaded onto boats that had been hauled up onto the beach. These then sailed to Carloforte to transfer their loads to larger cargo vessels. However, Porto Flavia enabled the ore to be transported directly from underground depots to the cargo ships by means of a conveyor belt (in the lower of the two tunnels).