The Ghost Cave is probably the most evocative submerged cavity in the entire karst panorama of the Alghero coast. The site was discovered in 1994 by the Alghero diver Marco Busdraghi, it presents unusual characteristics for sea caves. As with all caves with vertical limestone stratification, it is defined as penstock, the cavities were formed due to the combined effect of the limestone dissolution by the fresh water and its pressure. The presence of circular tunnels testifies to the ancient presence of fresh water that flowed within the massif.

The cave penetrates the wall about 70 meters and this determines its classification. The environments alternate large openings and narrow passages with outcrops on the surface and an internal lake in which it is possible to admire cascades of extremely suggestive calcite formations. The submerged parts testify to the modifying evolutions to which the cave has been subjected over the millennia,  there are 3 main phases:

The first was that of the creation of the cave when it was still in an aerial environment, with erosion and dissolution of the limestone due to the action of fresh water, followed by a second phase also in an aerial environment which saw the horizontal deposition of layers of calcite in some areas above deposits of clay and mud derived from previous erosion and dissolution, at the same time the formation of stalactites and stalagmites and columns occurred thanks to the fusion of these, the third phase, more recent was that of the "re-erosion" of the cave in the submerged parts, a phase which led to the destruction of the calcite formations which remained present in the surface areas. The calcite in this cave is bright white and semi-transparent, so much so that by placing the lamp behind some formations you can witness spectacular plays of light. In the shoreline, the eroded calcite resembles ice melting with warm water. Its "dolomitic" nature in a marine environment defines its preciousness in a scientific sense and its spectacular nature. The nature of the water inside determines the absence of life forms and therefore the consequent clarity unless the sediment or mud deposits scattered in various parts of the cave are moved.