" We were on the Congo’s eastern edge and, as the helicopter climbed higher, I could see nothing but an unbroken spread of vegetation. I was looking at the Congo’s rainforest, one of the natural wonders of the world. Conservationists describe it as one of the Earth’s lungs, an immense expanse of oxygen-generating green, matched in size only by the Amazonian rainforest. Explorers recorded it as one of the most impenetrable and hostile environments on the planet – as clammy as a pressure cooker, thick with disease, capped by a tree-top canopy too solid for sunlight to penetrate. "

― Tim Butcher , Blood River: A Journey to Africa's Broken Heart