Vava'u

A submerged sea cave on Nuapapu Island entered through an underwater passage invisible from the surface — divers swim a short "blind" passage (no confirmed sightline to the exit) into an air-filled inner chamber, where barometric swell creates a visible fog/mist effect. Sources describe a shallower snorkel-depth entrance (~3-4m) and a deeper scuba entrance (~12-16m, exact figure inconsistent across sources). No operator states a formal certification-card requirement in writing, but the physical and psychological demands of the blind swim-through make this a genuinely advanced-level dive, not a beginner one. Day boat from Neiafu, no liveaboard.

A large rock formation on Tu'ungasika Island split by a vertical fissure divers descend and swim through — a genuine wall/topography dive, distinct in character from Mariner's Cave's overhead passage. Nudibranchs and Christmas tree worms on the walls; occasional whitetip, blacktip, and grey reef shark sightings (not reliable enough to record as a structured wildlife entry). Operators have not published an exact maximum depth for this site — left unknown here rather than guessed. Day boat from Neiafu, no liveaboard.