The forest is home to half of all remaining mountain gorillas, along with chimpanzees, African elephants, honey badgers, golden cats and a menagerie of creatures. It's one of the most biodiverse ecologies on Earth, and also one of the oldest: When sub-Saharan Africa's climate cooled during the last Ice Age, Bwindi became a refuge. It's remained one ever since.

"It's not a joke that the word 'impenetrable' appears in the official national park name," said Badru Mugerwa, a researcher with the Institute of Tropical Forest Conservation.

Not only is the terrain jagged and mountainous, but Bwindi's dominant feature, "superseding even the impressively rich flora of noxious nettles, barbed briars and spiny Acanthus, is its remarkable density," said Mugerwa. "Walking these hills every day, recording what animals we come across, would be very tedious, close to impossible."