Gunung Leuser National Park represents several ecosystem types, from coastal forest ecosystem through tropical lowland forest ecosystem to montane forest ecosystem. Most of the Park area is covered with thick Dipterocarpaceae forest with rivers and waterfalls flowing through it. There are some endangered and peculiar plants, namely daun payung raksasa (Johannesteijsmannia altifrons), rafflesia flowers (Rafflesia atjehensis and R. micropylora), and Rhizanthes zippelnii-the biggest flower, with a diameter of 1.5 metres. In addition, there is one plant unique to the area: the ara, a strangling plant.
Endangered and protected animal species which inhabit the Park include orangutan (Pongo abelii), siamang (Hylobates syndactylus syndactylus), Asian elephant (Elephas maximus sumatranus), Sumatran tiger (Panthera tigris sumatrae), Sumatran rhinoceros (Dicerorhinus sumatrensis sumatrensis), serow (Capricornis sumatraensis), great hornbill (Buceros bicornis), sambar deer (Cervus unicolor), and leopard cat (Prionailurus bengalensis sumatrana).
Gunung Leuser National Park has been declared a Biosphere Reserve. Under a cooperation program between Indonesia and Malaysia, the Park is also designated as a "Sister Park" to the Taman Negara in Malaysia.
Gurah: fantastic views, valleys, waterfalls; animals and plants such as Rafflesia, orangutans, birds, snakes and butterflies.
Bohorok: an orangutan rehabilitation centre; ecotourism activities like kayaking/canoeing, camping, and birdwatching.
Kluet: boating on rivers and lakes, trekking through coastal forest and caving. Kluet is also a habitat of tigers.
Sekundur: camping, caving, animal observation.
Ketambe and Suak Belimbing: suitable place for research on primates and other animals; research facilities include accommodation and a library.
Gunung (Mount) Leuser (3,404 m asl.) and Mt. Kemiri (3,314 m asl.): mountain climbing and hiking.
River rafting along the Alas River: start from Gurah-Muara Situlen-Gelombang for a three-day trip.
Cultural attractions outside the Park include the Lake Toba Festival in June (held on the Lake) and the Malay Culture Festival held in July in Medan.
Best time of year to visit: June to October.