Ngorongoro Crater.

The Ngorongoro Crater is often called ‘Africa’s Eden’ and the ‘8th National Wonder of the World’, a visit to the crater is a main drawcard for tourists coming to Tanzania and a definite world-class attraction.

Within the crater, large herds of zebra and wildebeest graze nearby while sleeping lions laze in the sun.

Size: 8,300 sq km.

Within the Ngorongoro Conservation Area at the eastern edge of the Serengeti.
Getting there: 

Drive from Arusha, Lake Manyara, Tarangire.
What to do:

Besides vehicle safaris to Ngorongoro Crater, Olduvai Gorge, and surrounding attractions, hiking treks through the Ngorongoro Highlands within the conservation area
When to go:

Migration is December to July, but good to visit all year round

Lodges, Luxury Lodges, Tented Camps and Basic Camping.