Oldoinyo Lengai, the most sacred mountain of the Maasai, is an active volcano in the Eastern Rift Valley in North Tanzania, the furthest east remnant of the super volcano Ngorongoro that dominated Africa three millions years ago. It is the only volcano in the world that erupts natrocarbonatite lava, which is colored black but soon turns white when reacting to moisture in the air. Also, the temperature of the lava is much lower and the flow rate much slower than basalt, so it is possible to get much closer to the activity and people have referred to it as a "toy volcano".

The name comes from the Maasai language, meaning "Mountain of God", and it is a wonderful area for walking. The steep fertile slopes are home to a variety of small game which in turn support mid sized predators. Once the summit is reached, the sunrise can be spectacular. Fumaroles vent sulphurous gases and steam and from time to time ash cones erupt black ash with resounding thuds. A remarkable environment.