The large reef is in fact double and surrounds Grande Terre for 372 miles (600 km) each. The furthest offshore marks the ancient shores at the end of the Tertiary. Sometimes natural coves form and trap dark blue waters like the Oundjo hole. It is taboo for Kanaks and would mark the entry of souls to another world. No human shadow should fly over it under pain of great misfortune. It is therefore forbidden to approach it. The only one to have been authorized to dive into this sagging cave is Commander Cousteau. He never revealed what he had seen there.