Gruta da Pombeira

A RIB drops divers into a small, sand-floored bay below the cliffs, about ten minutes out from Cascais marina. The cave entrance sits at the back of the bay in water that averages 6 metres, and the passage runs west for roughly 10 metres at reduced height: wide enough to pass through with steady trim, tight enough that the rock closes in around you. A second opening breaks through to open sea at the passage's far end, but swell and shallow water make it unusable for entry or exit, so the dive goes in and out through the same sandy-bay mouth. Shoals of sea bream and wrasse move along the rock, octopus and cuttlefish work the crevices, and large conger eels sit back in the passage's darker stretches; pipefish turn up occasionally, though not on every visit. A dense barnacle colony crowds the rock near the entrance, the site's most distinctive feature.

Gruta da Pombeira is not the open rocky recess that gives Boca do Inferno its name a few minutes away, and it is not the reef that continues from it, still known here as Maria Alice. It is the passage between the two: a sandy bay, a run of low, close rock, and a return the way you came. Every source describing this coast agrees it is the dive rated for the least experienced diver aboard, built around the shape of the rock itself instead of a long reef swim.

No operator publishes a minimum certification for this cave, but it is not a beginner try-dive either: the centre running trips here dives every boat with an instructor or divemaster at up to four divers per guide, and keeps a different, shallower site nearby for first-time try dives. Inside the passage, hold trim and keep clear of the walls; brushing against the rock is unnecessary with steady buoyancy. At the far end, do not treat the second opening as a way out; swell reaches it and the water is too shallow to pass through safely. The site carries no marine-reserve status, permit or fee, and access is boat-only, with no shore-entry option.