CharmingSardinia.com suggests to visit the following sight in the Province of Sassari:
Anghelu Ruju Necropolis (Alghero)
Asinara National Park
Doria Castle and Elephant Rock (Castelsardo)
Nuraghe Santu Antine (Torralba)
Grotte di Nettuno (Alghero)
Archaeological and Historical Ethnographic Museum Sella and Mosca (Alghero)