The main beach near Castelsardo is at Lu Bagnu, just a few minutes by car west of the old town along the coast road. It is a long, sandy stretch with calm water and a small tourist development of bars and beach rental operations — nothing exceptional by Sardinian standards, but good for a swim and convenient to the town. Lu Bagnu can also be reached on foot from the lower part of Castelsardo in about twenty minutes.
The coast extends westward toward Valledoria at the mouth of the Coghinas River, where there is a longer and less developed beach. Eastward, the coast toward Portobello di Gallura has rocky coves that are best accessed by boat.