Marovo Lagoon is the largest lagoon on Earth enclosed by a double barrier reef, 700 square kilometres of water in the New Georgia group of the Solomon Islands, threaded with rainforest islets and villages on stilts, where there are no roads and no bridges and everything moves by boat. Most lagoons are closed off by a single line of reef; Marovo has two, an inner and an outer barrier, with islands raised on the reefs and a deep calm lagoon between them and the big islands of Vangunu and New Georgia, so that the water inside is sheltered, green over the shallows and blue over the deep, and the maze of it becomes legible from above, on a light-plane hop between the grass airstrips or from the top of an island ridge. Dugout canoes are paddled between neighbouring islets, larger boats call at the village jetties, and the guesthouses are small bungalows of sago-palm thatch on stilts at the waterline under coconut palms, run by families and reached only by water, like everything else; a night in one is a night in the village, with the fish from the lagoon.
The reef is the other half. Off any beach with a mask, or on the outer walls with a tank, the lagoon opens into terraced coral gardens, giant clams, clouds of reef fish and the sharks and rays of the passes, and the wrecks and aircraft of the Second World War lie in the water around the New Georgia group, where the Pacific war was fought. The villages of Marovo are known across the Pacific for their carvers, who work six local woods, from rare black king ebony to brown kerosene wood, into bowls, model canoes and figures, and ease slivers of pearly white nautilus shell into the wood until a pattern surfaces, on a shaded veranda with the lagoon behind. The lagoon has been proposed for UNESCO listing since the 1990s, and logging on the big islands is its threat. Marovo is a sea inside two reefs, and the villages on its water live by the canoe.