Ngorongoro is the largest intact volcanic caldera in the world: 19 to 20 km across, about 260 square kilometres of floor, and walls rising 400 to 600 m. It formed when a volcano estimated to have been higher than Kilimanjaro collapsed some two to three million years ago.
The floor
Around 25,000 large animals live inside, including one of the last accessible populations of black rhino in Tanzania, some 25 to 30 individuals. Because water and grazing are available year round, most animals do not migrate out. Lions here have suffered from inbreeding and disease because the crater is effectively an island; the population is around 60 to 70. Elephant bulls with exceptionally large tusks use the crater, but breeding herds mostly stay in the forest above.
Visiting
Descent is by two one-way roads and the ascent by a third; four-wheel drive is compulsory. Vehicles may enter for a maximum of six hours, and the crater is busiest between eight and eleven in the morning. Only the Ngoitokitok picnic site allows leaving the vehicle, and the black kites there will take food from your hand whether or not you offer it. Fees are high: a crater service fee per vehicle on top of the conservation area fee per person.
The Conservation Area
The crater sits inside an 8300 square kilometre multiple land use area, the only protected area in Tanzania where Maasai pastoralists graze cattle alongside wildlife. That arrangement has become contested, with relocations from the Loliondo and Ngorongoro divisions drawing international criticism. Visitors should be aware of the dispute rather than treat the landscape as empty.
Olduvai Gorge
On the road to the Serengeti, Olduvai, more correctly Oldupai, is where Mary and Louis Leakey found hominin remains spanning nearly two million years, including Paranthropus boisei in 1959 and Homo habilis in 1960. The small museum was rebuilt and is worth the stop. Nearby at Laetoli, Mary Leakey found a trail of footprints in volcanic ash made 3.6 million years ago by three individuals walking upright.
Empakaai and Olmoti
Two smaller craters in the highlands can be walked with an armed ranger. Empakaai holds a soda lake with flamingos and gives a view of Ol Doinyo Lengai, the only active carbonatite volcano in the world, whose lava is cool enough to be black. Very few visitors come here.