It's a story that I remember hearing years ago, but the details of which I had never seen until reading an article in the August 2019 National Geographic. In 1959 Tibetans feared that the Dalai Lama would be seized by the People's Liberation Army of China, so they engineered his escape from Tibet to India. The escape route entailed traveling upward from Lhasa, over passes at 15,000 feet altitude, then 16,000 x4, then 17,000 feet (5200 meters), over a period of two weeks, then gradually down to sea level in India, as indicated on the embedded graphics.
The magazine apologizes for using "variable scale" in the images, and I normally decry deceptive y-axes on graphs, but in this case I'll give them a pass because of the enormous problems in graphing Himalayan peaks to scale. What impresses me now is the awesome altitudes traversed, even granting that the participants had a lifetime's adaptation in terms of their heart, lungs and hemoglobin.