As a result, the Park consists of steep, almost inaccessible mountainous terrain, with altitudes that range from 0 meters in Kluet (South Aceh), to 3,381 meters on top of the Gunung Leuser (Southeast Aceh), after which the Park is named. The Park encompasses a number of what were then much smaller nature reserves: Nature Reserve Gunung Leuser, Nature Reserve Kappi, Nature Reserve Kluet, Sikundur Langkat Wildlife Reserve, Ketambe Research Station, Singkil Barat and Dolok Sembilin. The Alas River runs through the Park, thus dividing the Park into an eastern and western half.