Aitutaki sits inside a triangle of coral reef so shallow you can wade a long way across it. The water sorts itself into bands of aquamarine, jade and deep blue purely by depth, and from the air the whole lagoon reads as a map of its own floor. Geologists call it an almost-atoll: an old volcano still rises along the northern edge, while the reef it once anchored has grown into a rim roughly twelve kilometres to a side. The lagoon inside is only a few metres deep. About fifteen low sand islands — the motu — lie scattered across it, most ringed with palms and bright white beach. The best known is One Foot Island, Tapuaetai, a slender bar of sand more famous than Aitutaki itself. Fewer than two thousand people live on the main island, and it is reached by a short flight from Rarotonga.
Most visitors meet the lagoon from a small boat, hopping between motu and wading onto empty beaches. Where the water barely reaches your knees you can step out and walk to an island across the flats, your own shadow sliding along the sand below you. Small rays and reef fish scatter ahead as you go, and turtles and shoals of trevally work the coral in the deeper channels. On One Foot Island a one-room post office will stamp your passport with a footprint. The short climb up Maungapu, the volcano's 124-metre summit, lays the entire triangle out below you in every shade of blue. Outsiders have been coming a while: Captain William Bligh charted the island from HMS Bounty in 1789, weeks before his crew mutinied. Aitutaki was the first of the Cook Islands to take up Christianity, in 1821, and its churches still fill on Sunday mornings. From July to October humpback whales pass in deep water outside the reef, and boats run out to swim with them.