The black basalt watchtower at the northern end of Porto Ferro bay is one of the best-preserved Spanish coastal towers in Sardinia. It stands on a rocky promontory above the beach, and the views from the base — south along the bay, north toward the open sea — make the short scramble up worth it.
Torre Negra was built in the 16th century as part of the Spanish coastal defence network, a chain of towers designed to give early warning of corsair attacks. The name ("Black Tower") comes from the dark local stone used in its construction, which gives it a distinctly different appearance from the lighter limestone towers found elsewhere on the island. You can walk around its base and peer through the entry arch, though the interior is not accessible.