Bwindi is a rainforest on the mountains of southwest Uganda so thick that very little daylight reaches the ground, and almost half the mountain gorillas left on Earth live inside it. There is no substitute for going. No mountain gorilla has ever survived in a zoo; every gorilla anyone has seen behind glass is a lowland cousin. This forest and the volcanoes on the Rwandan border are the only two places the animal exists at all. Getting to a family takes anywhere from one hour to six, behind armed guides and trackers, up steep, dripping undergrowth that is exactly what the name refers to. Then it is sudden. A screen of leaves comes apart and a family is feeding a few metres in front of you. The hour goes fast: youngsters tumbling through the vines, a yawn, a thumped chest, the silverback's unhurried look that meets your own and moves on.
The forest keeps more than the gorillas. Its altitude range stacks lowland and mountain habitat in one park, so chimpanzees live in these trees too. They are wild and unhabituated, and stay a shape in the leaves. Birders come for a different prize. There are more than 350 species here, two dozen found only along the Albertine Rift, and guides who know the calls work Mubwindi Swamp for the African green broadbill. At first light cloud pools in the deep valleys and snags on the ridgelines, then thins and lifts as the sun warms the slopes, until ridge stands behind ridge. That is the impenetrable forest seen from outside instead of climbed through. The Batwa lived in it for thousands of years, and about four thousand of them were put out with no land and no compensation when the park was declared in 1991. On the Batwa Trail their descendants walk you back along the old paths, showing how they tracked animals, took wild honey out of the hives and made fire without matches — through the same wall you fought all morning.