Home to Gunung Leuser National Park — one of the last places on Earth where tigers, rhinos, orangutans and elephants share the same forest. The Bohorok River and Bukit Lawang are the access point for habituated Sumatran orangutans, while the more remote Ketambe Research Station offers the best chance at wild, unhabituated primates and deep-forest birding. This corner of Sumatra also holds the Tapanuli orangutan (Pongo tapanuliensis), the world's most endangered great ape, centred on the Batang Toru ecosystem south of Tarutung.
Kerinci Seblat National Park straddles West Sumatra and Jambi — Indonesia's largest national park and one of the best places on the island for Sumatran tigers, with active camera-trap programs and professional guides operating out of Sungai Penuh. The Harau Valley offers limestone karst birding and the chance at large mammals working forest edges near agricultural land. The Minangkabau highlands provide a cultural counterpoint to the wildlife, with some of Sumatra's most intact traditional architecture.
Riau and Jambi provinces hold what remains of Sumatra's lowland peat-swamp forest — degraded in places, but still supporting Sumatran tigers and the remnant population of critically endangered Sumatran rhinos at Bukit Tigapuluh. The Berbak-Sembilang complex protects some of the largest mangrove and tidal flat systems in Southeast Asia, important for coastal birds and estuarine crocodiles. Access is challenging but rewarding for dedicated wildlife travellers.
Way Kambas National Park in Lampung is the standout — it holds the best-accessible population of Sumatran elephants on the island, as well as the Sumatran Rhino Sanctuary (closed to visitors but running an active breeding programme). Bukit Barisan Selatan protects a long spine of the Barisan mountain range, with tigers and tapirs in the upland forest. The south coast offers leatherback turtle nesting beaches and productive offshore waters.