If Niagara is a roar and Iguazú is a thunderclap, Tumpak Sewu—literally “a thousand waterfalls” in Javanese—is an orchestral swell you feel in your chest. Cradled in a horseshoe-shaped ravine at the foot of Mount Semeru, this curtain of more than forty separate streams plunges 390 feet (120 m) into…