Geologists estimate that Mangaia is at least 18 million years old, making it the oldest island in the Pacific. It's the second largest of the Cook Islands and the furthest south. It rises 4,750 metres (15,600 feet) above the ocean floor, and has a central volcanic plateau. Like many of the southern islands in the Cooks, it's surrounded by cliffs of fossilised coral, called the makatea, in this case 60 metres (200 feet) high. It looks beautiful in the centre picture, but the coral is razor sharp. Mangaia is also honeycombed with caves like the one pictured right with its owner, Teremanuia Taukakuma.