The red rocks that guard the harbour at Arbatax are porphyry roughly 250 million years old, cleaved into blocks the colour of dried blood by quarrying that once supplied Genoese builders. They sit at the southern hinge of a coastline that has no road along it. From Santa Maria Navarrese north to Cala Gonone, the Baunei and Dorgali cliffs rise unbroken for some forty kilometres, and every cove between them — Cala Goloritzè, Cala Mariolu, Cala Biriala, Cala Sisine — is reachable only by water or by a long descent on foot. That single geographic fact created the maritime tradition that arbatax boat tours now formalise. The limestone here is Mesozoic, laid down when the Tyrrhenian basin was a shallow sea. Karst dissolution hollowed it, and the collapse of underground rivers produced the sea caves that pit the wall at waterline. Grotta del Fico takes its name from the wild figs rooting in its ceiling; until 1997 it sheltered the last confirmed Sardinian population of the Mediterranean monk seal, whose local name, bue marino, still labels the neighbouring cavern near Cala Gonone. Cala Goloritzè itself is younger than it looks: a landslide in 1962 opened the beach, and its 143-metre limestone pinnacle, the Aguglia, has drawn climbers since the 1980s. Protection followed recognition. Goloritzè became a national monument in 1995, and the Gulf of Orosei sits inside the Parco Nazionale del Golfo di Orosei e del Gennargentu, with daily landing quotas and a ban on anchoring over Posidonia meadows. The seagrass matters: Posidonia oceanica fixes the sediment that keeps the water its particular colour, a pale green over white pebble shelving to indigo where the shelf drops. Skippers work moorings, not anchors, and approach the beaches under electric or idle power. What matters today is that the boat has become the only honest way to read this coast. From the deck the cliffs are legible as one structure — a fault-scarp draped in juniper and euphorbia, punctuated by the ravines locals call codule, dry riverbeds that flood twice a year and fan gravel into the sea. Shepherds' paths thread above; the Selvaggio Blu trekking route crosses the ridge in eight days. A Gulf of Orosei coastal cruise compresses that into a single passage. Departures from Porto di Arbatax, 08048 Arbatax, Tortolì, cost nothing to reach — entry to the port is free at 0 EUR, with operators charging separately — and it is from that quay, between 08:00 and 18:00, that arbatax boat tours tours leave for the cliffs.