Tanzania’s Ol Doinyo Lengai volcano is unique in the world : its liquid black lava turns snow white when it cools down. Our distant ancestors left some footprints which were petrified by the volcano 20,000 years ago... Mathieu Kervyn, a volcanologist at the University of Brussels, is one of the rare specialists of this particular volcano. It has not been studied much due to its difficult accessibility. After a perilous climb, Mathieu reaches the magnificent crater in order to draw a map. At the foot of the volcano, on the shores of Lake Natron, the Maasaï people worship the God who sleeps in its smoking crater: the great Engai.