Set in Northern Tanzania, sharing part of the Serengeti plains to the north-west and with the towns of Arusha and Moshi, and Mount Kilimanjaro to the east, Ngorongoro forms part of the unique Serengeti ecosystem.
A major ecological survey of the Serengeti Reserve (which then included Ngorongoro) in the late 1950s resulted in the establishment of the Ngorongoro Conservation Area (NCA) in 1959.
This was a pioneering experiment in multiple land use where pastoralism, conservation and tourism could co-exist. At the same time the Serengeti National Park was enlarged and extended northwards to the Kenya border, where it borders the Masai Mara.
Subsequently awarded World Heritage Site and International Biosphere Reserve status, the NCA covers an area of 8292 sq km and ranges in altitude from 1020m to 3587m.
The terrain embraces several distinct habitats from open grasslands to mountain forest, and from scrub bushland to highland heath. The area contains sites of international palaeontologists and archaeological importance. Around 25000 animals live in the Crater throughout the year, whilst in the NCA as a whole the numbers can swell to more than 2.5 million, depending on the season.
The NCA aims to maintain the historic balance of people and nature in a way which has not been possible in many parts of Africa. At stake are the rich biodiversity and ecology of the Serengeti Plains and Ngorongoro highlands, the major palaeontologists and archaeological sites and the vital water catchment areas. Within all this, man and wildlife have to live together without harm or destroying each other's habitats.
Man and his ancestors have lived in the Ngorongoro ecosystem for more than 3 million years. Evidence of a regional hunter-gatherer culture dates back 17000 years and it is clear that various tribes have migrated in and out of the area, just as they have done in relatively recent times. By careful management and continuing research, the fragile balance between man and nature is successfully maintained.
Two main geological rifts run through the area. Nine volcanoes in the Ngorongoro highlands were formed during the past 4 million years. One of these, Oldonyo Lengai (Mountain of God) is still active.
Over millennia the ash and dust from each eruption has been carried by the winds to form the fertile soils of the Serengeti plains.
The earliest sign of mankind in the NCA is at Laetoli where hominid footprints are preserved in volcanic rock 3.6 million years old. Further north, Olduvai Gorge has yielded a wealth of hominid and animal remains.
The jewel in Ngorongoro's crown is a deep volcanic crater - the largest unflooded and unbroken caldera in the world - 19.2km in diameter, 610m deep and 304 sq km in area. The rich pasture and permanent water of the Crater floor supports a large resident population of wildlife of up to 25000 - predominantly grazing - animals. These include wildebeest, zebra, gazelle, buffalo, eland, kongoni and warthog. The swamps and forest provide additional resources for hippo, elephant, waterbuck, reedbuck and bushbuck, baboons and vervet monkeys. The steep inner slopes provide a habitat for dikdik and the rare mountain reedbuck. Jackals thrive in the crater and bat-eared foxes live in the short grass areas. Predatory animals - lion, leopard, cheetah, serval cats - live off the abundant wildlife, and large packs of hyena roam the crater, making their own kills and scavenging from others. The crater is a dynamic and constantly changing ecosystem and the numbers and proportion of some animals has fluctuated considerably over the past 30 years.
Lake Magadi is alkaline, caused by deposits of volcanic ash. The depth, never more than 3 metres, varies during the year and during the dry season it shrinks dramatically. The lake edges are favourite stalking grounds for golden jackals, lions and hyenas.
Lerai is a Maasai word for the tall yellow-barked acacias that dominate the Lerai Forest in the south-west of the Crater. Eland, elephant, vervet monkeys, bushbuck, tree hyrax, francolin, saddle-billed stork, vulture and eagle all coexist here. A picnic site is located in the forest.
Rising from Ngoitokitok Springs, the vast Gorigor Swamp is home to many waterbirds, where hippos lounge in the deeper parts and grazing animals come to drink.
Thanks to anti-poaching patrols, black rhino in the Crater are relatively safe and the numbers are approaching 20. Ngorongoro Crater is one of the few places in East Africa where visitors can be certain of seeing rhino.
Lions are abundant in the Crater. There are five main Crater prides of between 10 and 20 animals, each defending its own territory.
Only bull elephants descend regularly to the Crater floor. The large breeding herds wander throughout the forest rim where they find the most suitable food.
Cheetahs live in the Crater but sometimes find it hard to defend their kills against the many lions, so visitors may have a better chance of seeing these beautiful animals on the plains. Cheetah are the fastest land animals and can achieve speeds of nearly 115kph (70 mph)
Leopards are found in the forests and along the Munge stream, but they are solitary creatures, secretive and hard to spot.
The mixture of forest, canyons, grassland plains, lakes and marshes provide habitats for a wide range of birdlife. The wet months see the arrival of the Eurasian migrants at the open pools. White storks, yellow wagtails and swallows mingle with the local inhabitants: stilts, saddle-bill storks, ibis, ruff and various species of duck. Lesser flamingos fly in to feed from their breeding grounds at Lake Natron. Distinctive grassland birds - ostrich, kori bustards and crowned cranes - abound.
Much of the Crater floor is made up of grassland, and this supports a large number of plains animals and birds throughout the year, particularly kongoni, buffalo, wildebeest, zebra, gazelle, warthog, kori bustard, blacksmith plover, crowned plover, Cape rooks, crowned cranes and ostriches.
For thousands of years a succession of cattle herding people moved into the area, lived here for a time, and then moved on, sometimes forced out by other tribes.
About 200 years ago the Maasai arrived and have since colonised the area in substantial numbers, their traditional way of life allowing them to live in harmony with the wildlife and the environment. Today there are some 42000 Maasai pastoralists living in the NCA with their cattle, donkeys, goats and sheep. During the rains they move out on to the open plains; in the dry season they move into the adjacent woodlands and mountain slopes.
The Maasai are allowed to take their animals into the Crater for water and grazing, but not to live or cultivate there. Elsewhere in the NCA they have the right to roam freely.
The Gatoga, Nilo-Hamitic-speaking pastoralists, who arrived more than 300 years ago and were subsequently forced out of the Serengeti-Ngorongoro area by the Maasai, today live just outside the NCA in the Lake Eyasi basin and beyond.
Beyond the Crater:
While the Ngorongoro Crater is the single most visited site, the rest of the NCA offers many rewards fro those visitors prepared to explore further afield. Some of the attractions can be visited en route to Serengeti; other will require a special visit, but they are well worth the effort.
Located just outside the NCA, to the north-east near Lake Natron, this volcano, whose Maasai name means "Mountain of God" has had a major influence on the development of the area. Its ash has blown westwards onto the plains and helped shape the landscape and ecology. It is the only active volcano in the area, having erupted in 1966 and 1983.
Olmoti and Embakaai Craters:
Although smaller than Ngorongoro Crater, Olmoti and Embakaai to the north-east are noted for their beauty and solitude. The floors of both craters are easily accessible on foot, but visitors should be accompanied by a local guide.
The rim of Olmoti Crater is at 3700 metres but the crater itself is relatively shallow. The grassy caldera is home to eland, bushbuck and sometimes buffalo, along with the Maasai and their livestock. Water flows across the crater to the south side where it pours out through a cleft in a small but spectacular waterfall known at Minge stream.
The 300 metre deep, 6 km wide Embakaai Crater is dominated by a very deep soda lake which occupies nearly half the floor. Waterbirds such as the black-winged stilt, Cape teal and flamingo inhabit its shores. Much of the 32 km crater rim of Embakaai can be walked and provides spectacular views. Wildlife is often seen around the lake.
Gol Mountains (Oldonyo Gol Hills):
The remote and ecologically fragile Gol Mountains, with their pink granite cliffs, are divided by the grassy pass of Angata Kiti. In the rain shadow of the Ngorongoro highlands, this area is usually barren and dusty, yet it is exceptionally fertile and only a small amount of moisture produces mineral-rich grass that attracts huger herds of animals during the migration.
Northern Highland Forest Reserve:
The Forest Reserve extends in a wide band along the outer, southern and eastern slopes of the NCA. It is a mountain - not rain - forest and is a vital source of water for the wildlife and people of the NCA, as well as farmland to the south. The forest is home to elephant, buffalo, the elusive leopard and many birds. Visitors approaching Ngorongoro by the usual southern route will pass through part of the forest before arriving at the Crater rim where a viewpoint provides a stunning view of the caldera.
This remarkable black dune, composed of volcanic ash from Oldonyo Lengai, is being blown slowly westwards across the plains, at the rate of about 100 metres every 6 years. Some 9 metres high and 100 metres long in its curve, it can be found to the north of Olduvai Gorge.
This extremely alkaline lake is a major source of food for flamingos, which thrive on the algae which grows there. Lake Natron, just outside the NCA to the north-east, is the largest breeding ground in East Africa for flamingos.
A granite monolith rising 80 metres above the plains, Nasera Rock lies in the shadow of the Gol Mountains. During the wet season wildebeest romp across the green grass and baboons clamber up the steep sides of the rock. Klipspringers are resident on the rock and a wide variety of bird life is found in the trees near Nasera's base.
The Salei plains lead to Olkarien Gorge, a spectacular, narrow rocky cut at the eastern edge of the Gols, and the nesting site of the Ruppel's griffon vulture.
In the south-west of the NCA this forest-clad "bamboo mountain" is the source of the stream which tumbles into the Crater and supports the Lerai Forest. It supplies Ngorongoro village and the nearby lodges with drinking water, whilst its western flanks feed water into Lake Eyasi.
Bordering the south-western fringe of the NCA, the salty, sometimes dry, Lake Eyasi is rimmed by the steep wall of the ancient Eyasi Rift.
Laetoli and Olduvai Gorge:
At Laetoli, west of Ngorongoro Crater, hominid footprints are preserved in volcanic rock 3.6 million years old and represent some of the earliest signs of mankind in the world. Three seperate tracks of a small-brained upright-walking early hominid, Australopithecus afarensis, a creature about 1.2 to 1.4 metres high, were found. Imprints of these are displayed in the Olduvai museum.
More advanced descendants of Laetoli's hominids were found further north, buried in the layers of the 100 metre-deep Olduvai Gorge. Excavations, mainly by the archeologists Louis and Mary Leakey, yielded four different kinds of hominid, showing a gradual increase in brain size and in the complexity of their stone tools. The first skull of Zinjanthropus, commonly known as "Nutcracker Man", who lived about 1.75 million years ago, was found here.
The excavation sites have been preserved for public viewing and work continues during the dry season, coordinated by the Department of Antiquities.
The north wall of the Crater is covered by red thorn acacia, which is gradually taking over from the high mountain forest in the east. Steenbok are resident here, and you may also see elephant and giraffe, the latter never venturing into the Crater itself.
In the south-west of the NCA, between the treeless plains of the Serengeti and the escarpment near Lake Eyasi, is a band of acacia woodland. Fed by the Kakesio, and other small rivers, this area supports giraffe and a range of migratory plains animals.
The plains extend from Serengeti National Park into the western portion of the NCA, around the small lakes Ndutu and Masek to the north of Oldupai Gorge. The plains play their part in the annual migration which sees many animals head out of the area in May, when the long rains arrive, and northward into the Serengeti National Park.
Over half of the NCA is made up of vast tracts of open grassland - dry and barren for most of the year - swinging in an arc from Serengeti in the north-west, through the Gol Mountains, to the Salei Plains in the north-east.
Stretching westwards from the highlands and craters, the Salei Plains are lower and drier than the Serengeti, remote, harsh and thinly populated by the Maasai. Only the hardiest and most drought-tolerant animals stay on the dusty plains during the dry months, but is comes alive in the rainy season.
This mysterious ruined "city", at least 500 years old, is located just outside the NCA at the foot of the eastern escarpment. The long abandoned site includes remnants of an advanced irrigation system, terraced stone houses, and odd, rubble-filled platforms.
One of the world's most amazing sights is the annual migration of hundreds of thousands of plains animals - principally wildebeest and zebra - in a clockwise direction through the NCA, into the Serengeti, the Maasai Mara, and back into Ngorongoro again in search of fresh grazing and water as the seasons change. The animals usually move out of Ngorongoro around May when the Serengeti receives its rainfall and start returning to Ngorongoro around late November.