A chain of gorges separates Mount Kappa from the eastern side of the island. There is no bridge over them, and their depths hide the most pristine parts of the island's jungles. Scaling their walls looks like a complete folly, but maybe there are some mad daredevils in the world who could attempt it and live to tell the tale. In the overgrowth-covered bottoms of the area there might or might not be secret caverns hiding even more uncharted and untouched microworlds...
The origins of the Puahu River might be somewhere there.