The place
Mahale Mountains, in short.
Mahale is the hardest of these parks to reach and the one people talk about longest afterwards. Forested mountains rise straight out of Lake Tanganyika, and there is no road in — you fly to a strip and then take a boat along the shore to camp.
The chimpanzees are the reason. The Mimikire group has been followed by researchers since the 1960s and is habituated to people, which means a trek here can put you within a few metres of animals going about their day entirely unbothered.
It is also, simply, one of the most beautiful places in Africa: white sand beaches on a lake so clear you can see the bottom at ten metres, with rainforest behind and mountains above. Most people spend their afternoons in the water.