The crater was formed when a giant volcano collapsed millions of years ago, leaving a bowl that is complete enough to function as a self-contained ecosystem. Animals can come and go, but many remain on the crater floor all year because there is permanent water and grazing.

Ngorongoro is within the Ngorongoro Conservation Area, where Maasai pastoralists live alongside wildlife. The area also includes Olduvai Gorge, a key site in the study of human origins, and Laetoli, where fossil footprints of early hominins were found.

Because the crater is compact, you can see a lot in one day. A typical visit descends at dawn, spends several hours on the floor, then climbs back up for lunch on the rim.

Ngorongoro Crater is a volcanic caldera, the wide bowl left behind when a very large volcano erupted and then collapsed in on itself. Geologists place this roughly two to three million years ago, and estimates suggest the original cone was far higher than the rim you see today. It is often described as the largest unbroken caldera in the world, and it is part of the same chain of events that shaped the East African Rift.

The crater is about 18 kilometres across, with a floor of roughly 260 square kilometres. The steep walls rise around 600 metres from the floor to a rim at about 2,300 metres above sea level, while the floor itself sits at roughly 1,700 to 1,800 metres. The walls act like a natural enclosure that holds water, grass and a year-round supply of food, which is why such a large number of animals stay inside rather than migrating away.

Published estimates put the crater's resident large animals at around 25,000 to 30,000, mostly grazers such as wildebeest, zebra, eland and gazelle. The grazers support one of the densest predator populations anywhere. Lions and spotted hyenas are both thought to be among the most concentrated in Africa, and golden jackals, cheetahs and the occasional leopard can also be found.

• Black rhino. The crater is one of the best places in East Africa to see this critically endangered animal. Numbers fell sharply during the twentieth century and counts since have been small, in the tens rather than hundreds, so a sighting is a privilege and never a guarantee.
• Elephants. The resident elephants are mostly old bulls, often seen in or near the Lerai Forest.
• Lake Magadi. The shallow soda lake often holds flocks of flamingos, with hippos and many other waterbirds in nearby pools and swamps.
• Birds. Kori bustard, augur buzzard, long-crested eagle and many more can be seen on a single day.
• Who is missing. There are no giraffe, topi or impala in the crater, and no Nile crocodiles. This surprises many first-time visitors.

All of the Big Five can be seen, but leopards are hard to spot, so four of the five is a realistic aim for a day.

If you have a day to spare, the surrounding conservation area rewards exploration.

• Olduvai Gorge. A steep-sided ravine in the dry plains on the way towards the Serengeti, famous as one of the most important sites in the study of early humans. The Leakey family's discoveries here changed our understanding of human origins, and a small museum explains the findings. Nearby Laetoli holds fossilised footprints that date back about 3.6 million years.
• Ndutu. A lake and woodland area on the western edge of the conservation area, bordering the Serengeti. It is a centre of the calving season, usually around January to March, when the herds gather on the short-grass plains and predators follow.
• Empakaai Crater. A smaller caldera with a deep lake on its floor, reached on foot and best for travellers who enjoy walking and birdlife.

Ngorongoro is one of the most visited places in Tanzania, and the number of vehicles inside the crater at any time is limited by the authority, reportedly to around fifty. Early starts help you avoid the busiest hours, and a driver who knows the quieter loops makes a real difference.

Please follow the usual safari manners. Stay in the vehicle, keep your voice low, never feed or approach animals, and take all your litter with you. Respect the rules on the rim and in the surrounding villages, and ask before photographing local people. These small habits protect a place that is both a wildlife refuge and a home.

Ngorongoro is high and can be cold, particularly at night and in the early morning on the rim, where temperatures can fall close to freezing in the coolest months. The crater floor is warmer during the day, but it can be windy and dusty. Bring layers: a fleece, a warm jacket, a hat and gloves for the first drive, with lighter clothing underneath.

The drier months, roughly June to October, bring the clearest weather and good wildlife viewing. The greener months from around November to March are quieter, and birdlife is at its best. The long rains, usually around April and May, can make roads muddy and bring more cloud. Pack sunscreen, sunglasses, binoculars and a camera with a zoom lens, and keep a rain jacket handy in any season.

Figures were checked against more than one source. Where they disagree, such as lion numbers, fees and exact gate times, we leave out a precise figure. Please confirm current rules and prices with us before you travel.

• Ngorongoro Conservation Area (Wikipedia)
• Ngorongoro Crater (Wikipedia)
• Ngorongoro Conservation Area (UNESCO World Heritage Centre)
• Ngorongoro Crater safari planning guide (Duma Explorer)
• Exploring the Ngorongoro Crater (Insight Guides)