A sea cave accessible only by an underwater dive through a submerged entrance, making it more demanding than Swallows Cave but more dramatic. The underwater passage is about three metres below the surface and roughly three metres long — not technically difficult, but requiring confidence in the water and the willingness to dive into darkness. Most tour operators only take it on request and only with swimmers they are confident in.
Inside, the cave is a large air-filled chamber with sunlight filtering through the water below. The most remarkable feature is the pressure differential: each wave compresses and releases the air inside, causing a brief mist to form in the cave and then clear — a condensation effect visible every thirty seconds or so. The cave was noted by English sailor Will Mariner in his account of his years among the Tongans, published in 1817 and still the most detailed early European account of Tongan society.