Cape Marrargiu (or Marargiu) is a promontory on the north-western coast of Sardinia situated in the municipality of Bosa south of Alghero, on the so-called Griffon vulture coast, because of the very rare specimens of this species that nest there.

Capo Marrargiu is at the centre of a regional nature reserve for wildlife protection, of about 160 hectares, and is of particular importance for the quality and quantity of the protected and rare species it hosts.

The griffon vulture nests in these impervious coasts which represent its most important colonies in Italy. Among the other birds, the presence of rare species such as the golden eagle and the Bonelli’s eagle is remarkable, as well as the peregrine falcon, the Corsican seagull, the kingfisher and the royal kite.

The area is geologically characterised by a conspicuous presence of volcanic rock and a constellation of erosive caves, many of which open onto the sea. In some of these there were reported the sighting of specimens of monk seal, but there have never been certain data on the presence of this animal.

The reserve includes a biomarine park, which extends from the islet of Sa Pagliosa, in the north, to the river Temo (which crosses the town of Bosa), in the south.