The island of Sumba lies 250 miles east of Bali in the remote Indonesian province of East Nusa Tenggara. (The scheduled flight by regional jet from Denpasar to Tambolaka takes 55 minutes.) Until recently, even lifelong globe-trotters had seldom heard of it. With an area of 4,270 square miles — almost the same as that of Jamaica — and a population estimated to be around 760,000, Sumba is no mere tropical microdot. But for centuries, the island was isolated, undisturbed and practically unknown. A handful of Dutch colonizers came and went, leaving little permanent impression. Headhunting ceased only in the 1960s. Today, close to a third of Sumba’s people still practice an animist religion known as Marapu; an astonishing variety of languages is spoken; prominent individuals are still buried in megalithic tombs, familiar elsewhere as remnants of the Bronze Age; and each year during the rice-planting season, Sumbanese men engage in pasola, a ritualized battle on horseback. (Blood must be shed to ensure a successful harvest, and while nowadays the wooden spears are blunted, fatalities still occur.) Sumba began to attract a flicker of attention in the late 1980s, when surf enthusiast Claude Graves discovered a wave on the island’s southwestern coast, “Occy’s Left,” which is regarded by the cognoscenti as one of the best left-hand breaks in the world.