Grotta dei Fantasmi is a specialist overhead limestone cave dive in the Punta Giglio area near Alghero. White rock, air pockets, and narrow passages give the site a bright but serious cave feel. The route stays close to the surface once you are inside, so the dive rewards calm buoyancy and slow finning more than speed. It is a managed cave dive, not a casual swim-through, and the appeal is the geology and light rather than reef life.