The headland that closes the eastern end of Cagliari's bay is a fossil coral reef, laid down in the Miocene when this stretch of Sardinia lay beneath a warm shallow sea. Its silhouette does resemble a saddle. Local tradition explains the shape differently: the archangel Michael, so the legend runs, unhorsed Lucifer above the gulf, and the devil's saddle fell to earth as stone. The Italian name — Sella del Diavolo — has stuck since at least the medieval period. A sella del diavolo boat tour reaches ground that walkers cannot. The promontory rises roughly 130 metres above the water and drops on its seaward face in sheer limestone walls, pierced by caves and small inlets that are accessible only from the sea. Punic remains, a Roman-era cistern, and the ruins of a small temple sit on the summit plateau. Below them the Torre del Prezzemolo, a Spanish coastal watchtower, still marks the ridge. Military use closed much of the headland for decades; the area reopened to the public and today carries no gates and no fee — entrance is free, 0 EUR, since the Sella is a natural area rather than a ticketed monument. What the water adds is scale. From Marina Piccola the coastline unfolds in sequence: the marina basin, the cliffs of Calamosca, the Capo Sant'Elia lighthouse, then the long pale arc of Poetto beach and the salt pans behind it, where flamingos feed within sight of the city. The seabed here belongs to the Area Marina Protetta di Capo Carbonara's western approaches in character if not in boundary — Posidonia meadows, seabream, and visibility that regularly exceeds ten metres in settled summer weather. Snorkeling stops on the coastal boat trips take advantage of this. Cagliari has watched this rock for three thousand years. Phoenician sailors used it as a landmark; the Spanish fortified it; the Italian navy fenced it. Now the traffic is recreational, and the operators running a sella del diavolo boat tour from the city's marinas — with aperitif, with Prosecco, with snorkeling gear aboard — are the ones who keep the seaward face in public view. Among Cagliari landmarks, it is the one that looks most different from the water than from land.