Nereo Cave, submerged sea cave beneath Capo Caccia, Alghero, Italy

Nereo Cave is a submerged sea cave beneath the limestone cliffs of Capo Caccia, about 100 metres north of Neptune's Grotto. It extends roughly 300 metres in length, with tunnels and passages totalling about 500 metres, and has around ten entrances, arches and tunnels. Dives range from 0 to 35 metres through large tunnels and air chambers.

The cave takes its name from Nereus, a figure in Greek mythology regarded as an ancient deity of the Mediterranean Sea. The natural formation later became a destination for divers and marine researchers.

The cave draws divers from across the region who come to explore and observe marine life. It serves as a place where people develop appreciation for the underwater world and connect with efforts to protect it.

The cave lies under the limestone massif of Capo Caccia, about 200 m from Neptune's Grotto and a few kilometres from Alghero, inside the Capo Caccia marine protected area established in 2003. Its roughly ten entrances, arches and tunnels allow dives from 0 to 35 m, with air chambers and several possible routes. Because the two main entrances are far apart, plan the route with a local guide who knows the currents in the tunnels.

The cave was discovered several times in 1957 by air-tank divers who frequented the area while recovering World War II ammunition and hunting red coral. One of them, local diver Mario Musu, entered first in 1959 and detached 250 kg of coral from the vault.