Nereo Cave (Italian: Grotta di Nereo; Catalan: Cova de Nereu) is a huge underwater sea-cave situated on the north-west of Sardinia in the Coral riviera of Alghero, Italy. The name was given by the discovers in honour of the mythological figure Nereus, who is often billed as the Old Man of the Sea, father of the Nereids. The site is under the high limestone cliffs of Capo Caccia, 100 metres north of the famous Neptune's Grotto.