Neptune's Grotto by boat, forty minutes of cliffs and a lake beneath the rock.

The Grotta di Nettuno is a karst cave that opens to the sea at the base of the cliffs of Capo Caccia, about 24 km from Alghero. You can walk down by the Escala del Cabirol, but the arrival that made it famous is by sea: a boat leaves Alghero harbour, skirts the coast and drops you at a small quay at the mouth of the cave, almost at water level. From there you enter with a guide and walk a few hundred metres of the nearly two and a half kilometres the cave has.

The crossing

The boats leave from the Banchina Dogana, the quay on the harbour promenade, at the foot of the walls. The longest-running line is that of Navisarda, with a departure every hour every day until 31 October; the cave's website gives the start of the boat season as April. The Frecce delle Grotte line also runs, from the same quay. The crossing takes about 40 minutes: it passes Cape Galera, the cliffs of Punta Giglio, rounds Capo Caccia and the island of Foradada, a holed rock off the cape, and enters the cove of the cave.

Inside the cave

The visit is guided, starts every hour on the hour and lasts about 30 minutes. The route follows the shore of Lake La Marmora, a lake of clear salt water that fills a good part of the cave. You pass the Acquasantiera, a two-metre stalagmite with little pools of water; the hall of the Ruins, with large stalactites broken by 19th-century visitors; the Reggia hall, with calcite columns about nine metres high reflected in the water and an eighteen-metre ceiling; the Smith hall, with the Grande Organo, the largest column; and you finish at the Tribuna della Musica, a balcony over the lake.

Hours, price and tickets

The cave is open every day from 10:00 to 15:00 (last entry at 15:00) on the hours its website currently publishes; from 12 November to 18 March it is closed on Thursdays, and also on 24 and 25 December. If the sea is rough, it does not open. In high season the hours may be longer: check the official website before going.

Entry costs €18; €10 for ages 6 to 17 and for students up to 26; free for under-6s. The boat is paid separately: Navisarda does not publish the price on its website and you see it when you book or by phone. The cave recommends buying the ticket online on its sales platform; from June to October, if you arrive by boat, you can also buy at the harbour office.

Who it is for

For almost everyone: the boat avoids the 654 steps of the staircase. It is the option the cave itself recommends for families with children and older people. It is not wheelchair accessible. You do not go in wearing swimwear or barefoot, and there are no toilets inside: they are next to the ticket office.