Ol Doinyo Lengai means "Mountain of God" in Massai language. It is a steep around 2900 m high stratovolcano located in a section of the East-African rift valley in northern Tanzania, near the Ngorongongo and Serengeti National parks. The volcano is known for its unique type of natrocarbonatite lava and as such it is the only known active natrocarbonatite volcano on earth. In August 2003, Tom Pfeiffer together with Marco Fulle, Stephane Granier and Martin Rietze undertook an expedition to this volcano organized by Fred Belton, is a passionate and experienced climber of Lengai since many years and guides an excellent expedition. During our stay, the activity was generally at a low level, but remarkable by its explosive character, which is regarded unusual for Lengai. All activity was confined to two cinder cones (misleadingly called hornitos, named T56B and T58B), which showed variable activity of lava fountains and strombolian activity, interrupted by repeated and spectacular collapses of the cones themselves.