The 45-kilometer coastal corridor linking Cagliari to Villasimius unfolds along Sardinia's southeastern littoral, a limestone-and-granite seam where the Gulf of Cagliari yields to the Gulf of Carbonara. Operators departed from Via Roma's waterfront since the early 2000s, when the route emerged as the island's most trafficked day excursion. The passage navigates past Sella del Diavolo — Devil's Saddle — a jagged promontory whose Phoenician watchtower ruins mark the gateway between Cagliari's urban harbor and the archipelago of marine reserves stretching toward Villasimius. Daily departures chart a course past Poetto Beach's seven-kilometer strand, then round the protected waters of Capo Sant'Elia, where depth drops to 40 meters within a hundred meters of shore. The boat tour from Cagliari to Villasimius operates year-round, with peak frequency between April and October when water clarity exceeds 25 meters and surface temperatures reach 24°C. Zodiac and motorboat fleets — vessels ranging from 8-meter inflatables to 12-meter cabin cruisers — accommodate snorkeling stops at Cala Fighera and Punta Molentis, sites protected under Sardinia's regional marine park statutes since 1998. Underwater visibility reveals posidonia meadows, gorgonian corals, and the occasional loggerhead turtle migration corridor. Onboard services vary: prosecco tastings, aperitivo service, and bilingual marine ecology briefings appear across tour tiers. The coastline's geological signature — Cambrian limestone overlaid with Miocene sediment — creates the cove formations and karst grottoes that define the route's visual character. Cagliari coastal excursions trace a maritime corridor first documented in Roman portolan charts, later monopolized by Genoese trade galleys shuttling between the capital and the silver mines of Sarrabus. Modern operators follow the same offshore trajectory, maintaining a nautical distance of 200 to 500 meters from shore to preserve nesting habitats for Audouin's gulls and Eleonora's falcons. The journey duration averages 4 to 6 hours depending on tide schedules and wind conditions, with return routes timed to catch the western light illuminating the Sette Fratelli mountain range inland.