Tanzania comprises many lakes, national parks, and Africa's highest point, Mount Kilimanjaro (). Northeast Tanzania is mountainous, while the central area is part of a large plateau covered in grasslands. The country also contains the southern portion of Lake Victoria on its northern border with Uganda and Kenya. Administratively, Tanzania is divided into 30 regions, with twenty-five on the mainland, three on Unguja (known informally as Zanzibar Island), and two on Pemba Island. Physical Geography Northeast Tanzania exhibits a mountainous terrain and includes Mount Meru, an active volcano, Mount Kilimanjaro, a dormant volcano, and the Usambara and Pare mountain ranges. Kilimanjaro attracts thousands of tourists each year. West of those mountains is the Gregory Rift, which is the eastern arm of the Great Rift Valley. On the floor of the rift are a number of large salt lakes, including Natron in the north, Manyara in the south, and Eyasi in the southwest. The rift also encompasses the Crater Highlands, which includes the Ngorongoro Conservation Area and the Ngorongoro Crater. Just to the south of Lake Natron is Ol Doinyo Lengai with an elevation of , the world's only active volcano to produce natrocarbonatite lava. To the west of the Crater Highlands lies Serengeti National Park, which is famous for its lions, leopards, elephants, rhinoceroses, and buffalo plus the annual migration of millions of white bearded wildebeest. Just to the southeast of the park is Olduvai Gorge, where many of the oldest hominid fossils and artifacts have been found. Further northwest is Lake Victoria on the Kenya–Uganda–Tanzania border. This is the largest lake in Africa by surface area and is traditionally named as the source of the Nile River. Southwest of this, separating Tanzania from the Democratic Republic of the Congo, is Lake Tanganyika. This lake is estimated to be the second deepest lake in the world after Lake Baikal in Siberia. The western portion of the country between Lakes Victoria, Tanganyika, and Malawi consists of flat land that has been categorised by the World Wildlife Fund as part of the Central Zambezian miombo woodlands ecoregion. Just upstream from the Kalambo Falls, there is one of the most important archaeological sites in Africa. Tanzania's Southern Highlands are in the southwestern part of the country, around the northern end of Lake Malawi. Mbeya is the largest city in the Southern Highlands. The centre of Tanzania is a large plateau, which is part