This vast protected area stretches from Lake Natron in the northeast, to Lake Enyasi in the south, and Lake Manyara to the east. Eight million years ago, the Ngorongoro Crater was an active volcano but its cone collapsed, forming the crater that is 610 meters deep, 20 kilometers in diameter, and covers an area of 311 sq. km. Spectacular as it is, the crater accounts for just a tenth of the Ngorongoro Conservation Area. The crater is home to many species of wild game and birds. With the exception of impala and topi and the giraffe, almost every species of African plains mammal lives in the crater, including the endangered black rhino, and the densest population of predators in Africa. A strange thing is that the crater elephants are mainly bulls. The birdlife, which includes the flamingo, is mainly seasonal, and is also affected by the ratio of soda to fresh water in Lake Magadi on the crater floor. Views from the rim of the crater are sensational. On the crater floor, grassland blends into swamps, lakes, rivers, woodland and mountains. You can descend to the floor of the crater in a four-wheel drive vehicle. Only 4WD vehicles are allowed into the crater and game rangers are compulsory for all.