Gruta Azul

A flooded sea cave on the northwestern face of Ilha do Cabo Frio, one of Arraial do Cabo's most distinctive dives. At low tide an underwater arch at 6 meters leads into a cavern rising to an air pocket above, where indirect sunlight filters through and turns the water a luminous electric blue — the effect that gives the site its name. Visibility inside varies with upwelling pulses: on calm winter days the water can be 15 meters clear; in summer thermoclines can reduce it to 5. Spiny lobsters, moray eels, and bronze sweeper schools shelter in the ceiling cracks. Outside the cave a boulder slope drops to 20 meters with sea turtles, goatfish, and occasional Atlantic goliath grouper resting in the shade of large rocks. Appropriate for open water divers with a calm briefing on cavern etiquette; no overhead-environment certification required for the tourist zone.