piazza has been used for military commemorations, from Fascist gatherings and parades to present-day celebrations of national events. A renovation of Piazza Oberdan was proposed in April 1953; pavement slabs were laid and flower beds were arranged around the monument, which was fenced off with chains. In 1981, the piazza was resurfaced and its flower beds rearranged. Saint Barbara Cave Discovered in 1952, some scholars estimate that the cave dates back to the Silurian (between 444 and 416 million years ago). A tour takes about three hours; it begins on a small train which runs to a lift, which approaches a grotto. A spiral staircase leads into the interior. A large, elliptical room with a diameter of at its widest point and a height of , the cave has aragonite columns, calcareous formations in a variety of shapes and a pool in diameter. The cave is covered in concretions, and "organ pipes" are calcareous formations which reproduce the sound of an organ when touched. Cala Domestica Tower The tower was built for defence and counterattack on the furthest promontory of the coast between Portixeddu and Porto Paglia, above the harbour entrance, against Muslim invasion as part of a network of hundreds of towers and outposts built by the Spanish crown. The towers, equipped with cannons, would open fire while the watchtowers sent smoke signals or drumbeat warnings. A fortress in the shape of a truncated cone, high and in diameter, was constructed of calcareous stone ashlar. The doorway, about high, leads into a domed room about wide with six loopholes. Mineralogical Museum The museum was built in 1871, at the same time as the mining school, to complete the miners’ theoretical training. It has two rooms with about 3,000 items, one of the sector's most complete and valuable collections. The first room has samples from all over the world, including samples from the Paris basin. In addition to the mineral samples, there are examples of the tools used to extract them. The second room contains the nucleus of the collection, with underground minerals (now no longer obtainable) from throughout the region. The Liberty style display cases have grotesque and arabesque carvings and herms. Bays and beaches In Iglesias' littoral zone, ( from the city centre), are the following bays and beaches (listed north to south): Cala Domestica, with the Spanish tower Su Forru (the Oven) cavern Portu Sciusciau shore, with