Nyungwe is a mountain rainforest so old and so unbroken that a quarter of all the primate species in Africa live inside it. Thirteen kinds share these 1,000 square kilometres of folded hills in southwestern Rwanda, on the Burundi border, among them wild chimpanzees and the Rwenzori colobus. Cloud sits on the trees for much of the year, and morning mist pools between the ridges until the forest seems to have no ground at all. The ridgeline is also a continental divide: rain falling on one side ends up in the Congo, and rain on the other starts toward the Nile. One of that second river's furthest sources rises on Mount Bigugu, here in the forest.
The signature walk is the canopy bridge, East Africa's first: a 160-metre walkway of steel and plank whose longest span hangs 70 metres above the trees below. From it the green rolls away to the horizon, edged by tumbling waterfalls and, at the forest's rim, the bright tea fields climbing the surrounding hills. Chimpanzees are tracked at dawn, when the habituated families are still calling from their night nests and a guide can follow the sound. More than three hundred bird species live here, dozens of them found only along this stretch of the Albertine Rift, and butterflies drift through every clearing. The trails are steep, wet and often slippery, and the forest gives up its animals slowly, which is why most people plan two mornings rather than one.