Neptune’s Grotto (Grotta di Nettuno) is a short boat or coach ride away from Alghero. The cave was discovered by local fishermen in the 18th century.

The entrance to the grotto lies only around a metre above the sea level at the foot of the 110-metre-high Capo Caccia cliffs and the cave can therefore only be visited when the waters below are calm. A stairway cut into the cliff in 1954, the 654-step escala del cabirol (goat’s steps), leads from a car park at the top of the cliff down to the entrance. The grotto is also accessible via a short boat trip from the port of Alghero; these trips are arranged hourly during the summer, but less frequently during spring and autumn.
Inside are passages of lit stalactite and stalagmite formations, and a 120-metre-long saltwater lake, which is at sea level.

Under water all around there are many big marine caves which are great for scuba-diving, the bigger and the most famous is the Nereo Cave.