Below the limestone promontory of Capo Caccia, at a depth of between 15 and 30 metres, there is a hidden underwater world, with a unique charm. Nereo’s Cave is the largest underwater marine cave in the Mediterranean and in all of Europe, with a 300-metre-long main tunnel and a series of secondary chambers that allows it to reach a total of half a kilometre in length. The cave is part of the protected marine area of Capo Caccia – Isola Piana, a ‘treasure trove’ of biodiversity, also included in the Park of Porto Conte, in the territory of Alghero. The park is a natural oasis of inestimable value due to the wildlife within it, as well as the breathtaking landscapes.

Nereo’s Cave has three main entrances, one at Punta dell'Asino, that leads to the front cave, which is the ‘accessible’ part, even for divers who are not highly specialised in speleology but do have some familiarity.