In the locality of Su Pranigheddu de S’Unighedda stands the nuraghe Costa or “Sa Regia”, which constitutes the most important example of nuragic architecture of the Goceano (upper Tirso valley). The nuraghe is defended by an imposing defensive wall and by a village partly situated within the area delimited by the defensive wall and partly on the exterior.

The defensive wall is formed of cyclopean masonry, made of large polygonal basalt blocks. This curving wall, is of the towered type and incorporates at least three towers, one at each end of the structure and a central one. The wall also has a walkway on the top. The nuraghe comprises a keep, two towers and a central courtyard. The main basalt tower was entered through a rectangular opening facing west which led into a 4m long corridor, with a spiral staircase on the left and a chamber at the end. This keep had an upper floor, of which the circular chamber with a niche is visible. Access to the two secondary towers situated in the southern part of the monument was gained from the oval courtyard. The entrance to the courtyard was situated to the south-west in the curtain wall between the two towers.

The village was formed by at least 29 hut-like structures, visible above ground level. They were circular constructions of polygonal basalt blocks. Between the nuraghe and the defensive wall there were four huts, whilst the majority of these dwellings were situated outside the defensive walls, to the west. Finds of bronze material during the latest excavation campaign, including a serpentine fibula, datable to the late Bronze Age-early Iron Age give a chronology and suggest, considering the prestige of the artefact, that the structure in which it was found (structure 4) belonged to an individual of rank and had been used (if only briefly) as a dwelling, as the presence of a hearth seems to indicate. As regards structure 9, its situation on the edge of the group of huts, its plan (which differs from the circular ones present on the site) and its careful construction together with the finds recovered, suggest that it was probably used for cult purposes. (MiBAC)