The critically endangered Sumatran orangutan (Pongo abelii) now only inhabits the northern tip of Sumatra, with roughly 7,500 individuals remaining — far fewer than its Bornean cousin. The UNESCO-listed Gunung Leuser National Park is the main sanctuary, reached via the riverside village of Bukit Lawang, about three hours northwest of Medan. Unlike Borneo's gentle boat tours, Sumatra delivers an intimate, physical experience: steep, humid jungle treks on foot where visitors walk the same ground as semi-wild apes. The fruiting season (June and July) brings orangutans closer to the trails, and Thomas's leaf monkeys, gibbons and hornbills are near-constant companions. The third, rarest species — the Tapanuli orangutan, recognised in 2017 — survives only in the Batang Toru forest further south, with fewer than 800 individuals.
