There is a description of three waterfalls, the middle one being described as a doorway, a portal into the inner, secret Pemako. It seemed to me that if this waterfall were so strong a feature of the landscape that they could envision it as a gateway to a hidden paradise, then this was a waterfall worth trying to find. You drive about three days east of Lhasa to a point halfway between the eastern border of Bhutan and the western border of Burma, right where the Tsangpo River makes a great bend and flows south into the jungles of Arunachal Pradesh. From there you walk days and days through any number of different passes that lead you over the eastern ramparts of the Himalayan range, down into this subtropical region off the Tibetan Plateau. It's an extremely wet rain forest, full of leeches and pit vipers.
Camping is very difficult.
Often we excavated for hours to make a place to put up a single tent. Some areas of Pemako have the densest population of Bengal tigers left in the world. The local people are Lobas, fierce animistic warriors who were converted to Buddhism by early lamas. They live in little villages perched on high terraces above the Tsangpo. Your discovery has been challenged by other explorers.