Stephan Mantel was on a quest. As he disembarked from the third flight since leaving Amsterdam, the tropical heat enveloped him. He had arrived in Putussibau, in the heart of Borneo, Asia’s largest island. A local guide and two hired helpers joined him for an hour-long journey along tributaries of the Kapuas River. Their boat, made from a hollowed-out tree trunk, sat so low that Mantel could trail his hand in the water. They docked and trekked deeper into the wilderness, where a thick layer of leaf litter and decay…
