Mediterranean · Italy
Capo Caccia & Nereo Cave
The Mediterranean's largest sea cave, with entrances from 8 m to 33 m
The limestone headland of Capo Caccia, near Alghero, drops 200 m into the sea and is hollowed through by the Grotta di Nereo, the largest sea cave in the Mediterranean — several hundred metres of interconnected tunnels with multiple entrances between 8 and 33 m. Divers pass through chambers hung with red coral and cup coral, surfacing in air pockets, and can complete circuits without ever leaving the daylight. Outside the cave, the cliff face continues underwater as sheer wall.
About diving in Capo Caccia & Nereo Cave
The cape sets the timetable. It faces the open north-west with nothing in front of it, so Alghero operators watch the forecast and take the cave days as they come; on a settled morning boats run the short distance under the cliffs to Nereo, and on a blown-out one they work sheltered water instead. A few wall sites can be entered from the shore, which is useful for filling a second dive, but the signature diving is boat-based.
What Nereo asks for is order rather than nerve. Operators run it in small groups behind a guide who knows which openings connect, and the sequence matters: with entrances spread between 8 and 33 m, the route is planned to work up towards the shallower exits rather than wander. Redundant lights are expected, and so is the buoyancy to move through a passage without putting a fin into growth that took decades to form. Without cavern training behind you, the walls outside are the better use of the day.
Those wall dives stand up on their own. Punta Cristallo and the falaise are vertical limestone worked as slow drifts with the stone on one shoulder and red gorgonians on the deeper sections, while the pierced islet of Isola Foradada is the easier option, a swim-through at about 15 m that also works as a night dive. The area suits divers who already hold cavern training or want a reason to get it, and photographers after red coral without going technical; anyone content on a wall still gets a full trip out of it if the cave is shut.
Best time to dive Capo Caccia & Nereo Cave
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Season | Fair | Fair | Fair | Good | Good | Prime | Prime | Prime | Prime | Good | Fair | Fair |
| Sea surface | 15°C59°F | 14°C57°F | 14°C57°F | 15°C59°F | 18°C64°F | 22°C72°F | 24°C75°F | 25°C77°F | 24°C75°F | 22°C72°F | 19°C66°F | 16°C61°F |
| Daytime high | 16°C61°F | 16°C61°F | 18°C64°F | 21°C70°F | 24°C75°F | 29°C84°F | 30°C86°F | 31°C88°F | 28°C82°F | 25°C77°F | 22°C72°F | 18°C64°F |
| Rain | 66 mm2.6 in | 61 mm2.4 in | 52 mm2.0 in | 50 mm2.0 in | 42 mm1.7 in | 22 mm0.9 in | 13 mm0.5 in | 18 mm0.7 in | 42 mm1.7 in | 63 mm2.5 in | 117 mm4.6 in | 78 mm3.1 in |
| Jan | Feb | Mar | Apr | May | Jun |
|---|---|---|---|---|---|
| Fair | Fair | Fair | Good | Good | Prime |
| Sea surface | |||||
| 15°C59°F | 14°C57°F | 14°C57°F | 15°C59°F | 18°C64°F | 22°C72°F |
| Daytime high | |||||
| 16°C61°F | 16°C61°F | 18°C64°F | 21°C70°F | 24°C75°F | 29°C84°F |
| Rain | |||||
| 66 mm2.6 in | 61 mm2.4 in | 52 mm2.0 in | 50 mm2.0 in | 42 mm1.7 in | 22 mm0.9 in |
| Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|
| Prime | Prime | Prime | Good | Fair | Fair |
| Sea surface | |||||
| 24°C75°F | 25°C77°F | 24°C75°F | 22°C72°F | 19°C66°F | 16°C61°F |
| Daytime high | |||||
| 30°C86°F | 31°C88°F | 28°C82°F | 25°C77°F | 22°C72°F | 18°C64°F |
| Rain | |||||
| 13 mm0.5 in | 18 mm0.7 in | 42 mm1.7 in | 63 mm2.5 in | 117 mm4.6 in | 78 mm3.1 in |
2011–2025 averages. Sea surface: NOAA Coral Reef Watch, measured at the surface, so deeper water can run colder. Daytime high and rain: NASA POWER.
May–Oct is the settled season; winter mistral and north-westerlies make the exposed cape unworkable for weeks at a time.
Best months: June, July, August, September
Capo Caccia water temperature and weather by month
The sea surface runs from 14 °C (57 °F) in February to 25 °C (77 °F) in August. It is 24 °C (75 °F) or warmer from July to September. Most rain falls from October to March, peaking at about 120 mm (4.7 in) in November; June to August are the driest. Daytime highs reach 31 °C (88 °F) in August and drop to 16 °C (61 °F) in January. The coldest water here is about 14 °C (57 °F), so pack a 7 mm suit with a hood, or a semi-dry.
Dive types & marine life
Groupers patrol the wall ledges and are boldest in the prime June-to-September window, when barracuda and reef-fish shoals gather off the cape. Inside the tunnels it is macro work in torchlight, with nudibranchs and small invertebrates on the rock — but through the fair shoulder and winter months boats reach the exposed cape only on settled days.
- Cave & cavern
- Wall
- Reef
- Night
- Groupers
- Octopus & cuttlefish
- Nudibranchs
- Reef fish swarms
- Macro critters
- Barracuda
Best dive sites in Capo Caccia & Nereo Cave
Cave & cavern
White limestone tunnels, air pockets and an internal lake
Cave & cavern
Two entrances, at 5 m and 12 m, below the 654-step Cabirol stair
Cave & cavern
Submerged stalactites and the old sea-level line, past the 7 m entrance
Red coral and cup coral inside the Mediterranean's largest sea cave
Artificial reef
Sheltered from the mistral, so it dives when the wind is up
Wall
A hundred metres of wall strung with arches facing the blue
Two rock towers on a 30 m bottom, and a wall passage at 5 m
Cave & cavern
Arches and life-covered walls, finishing in a cave at 8 m
Pinnacle
A pinnacle rising from 22 m in the middle of Baia d'inferno
Punta Cristallo
Sheer limestone wall dropping past 40 m with red gorgonians.
Falaise di Capo Caccia
The cliff face continued underwater, dived as a deep wall drift.
How to get to Capo Caccia & Nereo Cave
Alghero-Fertilia airport is a short drive from Alghero itself, which is where nearly everyone bases; Olbia and Cagliari work with a longer transfer. Boats leave from Alghero and from the sheltered bay of Porto Conte under the cape. Some walls go from shore, but Nereo is reached by boat.
Photos from Capo Caccia & Nereo Cave
Marco Busdraghi · CC BY-SA 3.0
Cqui · CC BY-SA 3.0
Dive videos
Cave Diving 05 GROTTA DI NEREO (Nereo's Cave) by © Antonello Porchedda · Antonello Porchedda Fotografia on YouTube
Photo credits
- Sheer limestone cliffs of Capo Caccia rising from deep blue sea, lighthouse on top by Teresa Grau Ros from Barcelona, CC BY-SA 2.0, via Wikimedia Commons
- Rugose squat lobster with long red arms among pale pebbles inside the Nereo Cave by Marco Busdraghi, CC BY-SA 3.0, via Openverse
- Stalactite-hung chambers and still water inside Neptune's Grotto at Capo Caccia by Cqui, CC BY-SA 3.0, via Wikimedia Commons
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