extinct volcanic caldera in the Eastern (Great) Rift Valley (East African Rift System), northern Tanzania. It lies 75 miles (120 km) west of the town of Arusha. The caldera measures between 10 and 12 miles (16 and 19 km) across and has an area of 102 square miles (264 square km). Its heavily forested rim rises 2,000 feet (610 metres) above the caldera's floor to an elevation of 7,500 feet (2,286 metres). Ngorongoro is thought to have formed about 2.5 million years ago from a large active volcano whose cone collapsed inward after a major eruption, leaving the present vast, unbroken caldera as its chief remnant.

The caldera's floor is predominantly open grassland. It is home to a diverse array of animals including elephants, black rhinoceroses, leopards, buffalo, zebras, warthogs, gnu (wildebeests), Grant's and Thomson's gazelles, and the densest population of lions in the world. The local Masai (Maasai) people also graze their livestock in the crater. Lake Magadi (Magadi, Lake), a shallow soda lake ringed by extinct volcanoes, is renowned as a habitat for great flocks of pink flamingos.