The Sardinian coastline is serrated by deep-cut coves of sparkling sea, surrounded by rocky prominences and edged in lovely strands of beach. The Aga Khan fell in love with the place, and dubbed it the Costa Smeralda, creating a magnet for the global glitterati. At Golfo Aranci, shining arcs of silvery sand are linked into a larger curve, encircled by a muscular peninsula that looms protectively between the town and the sea. It looks expensive, and it is.