Ngorogoro Crater

The  was an area in the Great Rift Valley of Africa. The Seventh Doctor took Ace there in March 1926. It was a natural habitat whose high walls prevented the animals within from crossing to the wider world outside. It was a natural habitat for lions, gazelles, buffalo, zebra, elephants and rhinos, amongst other large mammals.

On his March 1926 trip, the Doctor was reminded of another trip in which he'd witnessed the shooting of the last lion on Earth. Ace, for her part, was initially unimpressed with the area, until a Maasai chief named Naikosiai took her on a personally guided tour of the crater. She came away impressed not only by the large game animals but also the "hundreds and thousands of termite nests". (DWM: Prelude: Birthright)

Behind the scenes
The name used in real life is Ngorongoro.