Taman Nasional Gunung Leuser (TNGL), or normally called just "Leuser", covers app. 1.094.692 Hectares. The main part of the park is in the province of Aceh, but the park stretches into North Sumatra in the regencies of Langkat, Karo and Dairi. Leuser is the last place on earth where elephants, rhinos, tigers, clouded leopards, and orangutans are found within one area. Leuser has two major river systems, two major volcanoes and three lakes.

The Alas River cuts the park in a western and an eastern half. The driest months are February and June/July and the wettest March/April and September to November. 45% of all recorded plant species in the West Indo-Malayan region are found in Leuser. There are around 700 animal species living in the park. Between 300 and 400 of them are birds. About 8.500 plant species grow in the park, including the biggest flower in the world, Rafflesia Arnoldi. Two million people depend on the area as their water resource.

Leuser is not only unique for its richness in wildlife but also for its history. The first efforts to conserve Leuser arose from the surrounding communities. In 1934 the first document officially protecting Gunung Leuser was signed. In 1980 it was established in its present form. However, due to corruption illegal logging and animal poaching still threaten Leuser.