Cagliari's southern coastline holds a 14-kilometre stretch of protected marine habitat where water clarity exceeds 30 metres during settled weather. The Gulf of Angels wraps around Sella del Diavolo — Devil's Saddle — a limestone promontory that divides the urban waterfront from a series of secluded coves accessible only by boat. Phoenician traders charted these waters in the eighth century BC, establishing Karalis as a resupply harbour on routes linking Carthage to the Iberian Peninsula. Roman engineers later fortified the headland, and fragments of their signal tower remain visible on the saddle's eastern ridge. Snorkeling sardinia cagliari excursions depart from Marina Piccola and Poetto Beach between April and October, with morning departures capturing peak visibility before afternoon winds disturb the seabed. The Gulf's posidonia meadows — UNESCO-protected seagrass ecosystems — host octopus, cuttlefish, damselfish and occasional Mediterranean moray eels. Limestone cliffs descend vertically into water that transitions from turquoise shallows at three metres to cobalt blue beyond the 15-metre contour. Local operators concentrate on five primary dive zones: Cala Fighera, Cala Mosca, Calamosca Bay, the outer reef off Devil's Saddle, and the submerged rock formations below Punta Sant'Elia. Each site presents distinct topography — Fighera's sandy channels suit beginners, while the saddle's wall dives reward intermediate swimmers with deeper coral formations and larger pelagic fish. Sardinia's coastal boat trips incorporate snorkeling with cultural context. Guides explain how volcanic activity shaped the Gulf's submarine ridges 30 million years ago, and how the island's geographic isolation created endemic marine species found nowhere else in the Mediterranean. Cagliari's position at the centre of the Tyrrhenian Sea creates convergence zones where nutrient-rich currents support dense plankton blooms, which in turn attract seasonal visitors — tuna, swordfish and dolphin pods — between May and September. The water temperature holds at 18–24°C through the primary season, eliminating the need for full wetsuits except during early spring charters.