Olduvai Gorge — technically the Oldupaai Gorge in Maasai — sits just outside the Serengeti's southern boundary in the Ngorongoro Conservation Area, a steep ravine cut 90 metres deep by an ancient stream into volcanic sediments that preserve an extraordinary record of human evolution. The Leakey family worked here from the 1930s onwards, finding the fossils and stone tools that established eastern Africa as the cradle of humanity.
The small site museum is modest but excellent, with displays on the excavations, the hominid fossils (mostly casts), and the stone tool traditions — Oldowan and Acheulean — that were identified and named here. Staff lead guided walks into the gorge that take about 45 minutes. The site is best visited as part of a circuit through the northern parks — Serengeti, Ngorongoro, and Olduvai together make logical sense — rather than as a standalone destination. The gorge itself has a haunted quality that no photograph adequately captures: you are standing in a shallow trench where the ancestors of every human being alive today once made their tools.