The volcano that collapsed to form Ngorongoro is thought to have stood higher than Kilimanjaro before it fell in on itself some two and a half million years ago. What remains is a caldera nineteen kilometres across and roughly 610 metres deep, its floor holding about 260 square kilometres of grassland, soda lake and fever-tree forest. Travellers who take 3-Day Serengeti and Ngorongoro Safari from Zanzibar tours cross, in about ninety minutes of flying, between two entirely separate Tanzanias: coral coast and volcanic highland. Serengeti National Park was gazetted in 1951, the first in the country. Its name descends from the Maasai word siringet, the place where the land runs on forever. UNESCO inscribed the park in 1981; the Ngorongoro Conservation Area, established in 1959, had been listed two years earlier. Bernhard and Michael Grzimek's 1959 film Serengeti Shall Not Die argued the case for those boundaries. Michael died in a light-aircraft crash that same year and lies buried on the crater rim. Ngorongoro remains unusual among protected landscapes: Maasai pastoralists graze cattle inside it by right, sharing rim and floor with lion, elephant and one of East Africa's last viable black rhino populations. The region also holds one of the deepest records of human origins anywhere. At Olduvai Gorge, on the road between crater and plains, Mary and Louis Leakey uncovered the skull of Paranthropus boisei in 1959, dated to about 1.8 million years. Seventeen years later, at nearby Laetoli, Mary Leakey traced hominin footprints pressed into volcanic ash some 3.6 million years old. The Serengeti safari tour circuit therefore runs through both the largest surviving terrestrial mammal migration — roughly 1.5 million wildebeest, joined by 250,000 zebra — and the ground on which upright walking was first demonstrated. Ecologically the two areas work as one system. Volcanic ash from Ol Doinyo Lengai fertilised the short-grass plains of the south-east, producing calcium-rich pasture that draws the calving herds each February. Rain then pulls them north toward the Grumeti and Mara rivers by June, and back again with the storms. Conservation revenue underwrites the arrangement: the entrance charge across the Northern Circuit is 70 USD, a conservation fee per adult, per day, quoted as a typical rate that varies by season, and gates operate 06:00–18:00 every day of the week. A 3-Day Serengeti and Ngorongoro Safari from Zanzibar tour compresses that geography — coast, escarpment, caldera, plain — into three days, which reads less as an abbreviation than as a cross-section of East Africa.