Africa's Great Rift Valley runs four thousand miles from the Red Sea to the mouth of the Zambezi - a diverse landscape of erupting volcanoes, forest-clad mountains, spectacular valleys, rich grasslands and mighty rivers. Home to the greatest concentration of animals on Earth - lions, crocodiles, elephants, hippos and flocks of flamingos - and pastoralists such as the Maasai - this is a land in constant geological turmoil. Great Rift takes you to another world - a world of exotic extremes, where the forces of nature have shaped the landscape and so created a hotbed of evolution.