The Protected area of Capo Caccia - Piana Island falls within the territory of Alghero and includes Porto Conte bay and the stretch from Punga Giglio to Capo Caccia.
Some nature and archaeological sites include Le Prigionette, a forest with white donkeys, Giara ponies and deer, and the Grotta Verde, where there are traces from seven thousand years ago, perhaps intended for the dead or as grave goods.
In the park there are the Nuraghic complexes of Palmavera and Sant'Imbenia and the Roman remains of Villa di Sant’Imbenia and the Bridge over the Calich. The paths in the marine area lead up to panoramic views such as Cala della Barca, named for a French vessel that sank here in 1664.
On the seabed, among the crevasses and spires, you can observe impressive layers of calcareous algae and posidonia meadows, with fish, molluscs and crustaceans. Enormous massifs plunge into the sea with walls dotted with caves high up in the air and in the sea.
The Grotta di Nettuno offers suggestive scenery with stalactites and stalagmites and a lake. The underwater Grotta di Nereo is the largest in Europe: the entrance is 32m underwater and the exit is 15m down, after a 350m swim through tunnels and rooms. There are also the Grottoes of Giglio, Pozzo, Falco and the Tunnel Azzurro (blue tunnel) that crosses the promontory from Cala della Barca to Cala Puntetta.