Boca do Inferno

Boca do Inferno is a coastal dive: the boat drops divers along a rocky shoreline and follows it, staying close to shore instead of striking out into open water. Near the surface, small gorges cut into the rock, tight enough that their walls close in before opening out again. The reef steps down gradually from there, and by 16 metres it has given way to sand, the point where most dives turn back. There is no wall and no sudden drop, just a steady, readable slope that keeps navigation simple even on a first boat dive. Above the water sits the reason for the name: the Boca do Inferno chasm, a well-known coastal landmark, visible from the boat on the way out and a fixed point for orientation on this stretch of coast.

Boca do Inferno is one of several named dives near Cascais, each with its own character. Ten minutes along the same coast, Gruta da Pombeira threads an actual cave passage; further out, Tubos drops past 26 metres for experienced divers only. Boca do Inferno itself never leaves Open Water limits: the dive stays shallow throughout and there is no passage to route through, only coastline to follow. What it shares with the landmark above is only the name: the dive runs along the coast beside the chasm, not through it, so nobody should come expecting a swim into the rock recess itself. Two separately run operators send trips here. That is common on this coast, not a mark of Boca do Inferno standing apart from its neighbours. What does set it apart is what sits above the water: a recognisable Cascais landmark, visible on the boat ride out, that no other named site on this coast pairs its dive with.

The exact departure point for this dive is not fully settled: one base is given as Estoril, another as central Cascais, so treat your booking confirmation as the guide, not the map. A second, yacht-club-based centre also linked to this site is the alternative option. Groups are typically capped at a 4:1 diver-to-guide ratio, with a private guide available for an extra EUR 50 a dive. Conditions here can turn with the swell noted above, so it is worth checking with the centre before booking, even on a dive that itself runs along sheltered rock. No permit, reserve fee or diver quota applies here or anywhere on this stretch; the cliffs above sit inside the Sintra-Cascais Natural Park's boundary, a scenic and landscape designation, not a marine one.