Until little more than a century ago, this place was unknown outside China. But then news reached the West of a mysterious, hidden world of the orient. Hidden among the mountains, a lost Shangri-la paradise.
Western high society, in the grip of a gardening craze, was eager for exotic species from faraway places.
This gave rise to a new breed of celebrity adventurers, intrepid botanist-explorers known as "the Plant Hunters".
Yunnan became their Holy Grail.
The most famous was Joseph Rock, a real life Indiana Jones.
Remarkable film footage captured his entourage on a series of expeditions, as they pushed into the deepest corners of Yunnan.
In glorious colour he recorded the plant life he found on special photographic glass plates.
Sending thousands of specimens back to the West, the Plant Hunters changed the gardens of the world forever. Rock's success was born of a massive effort.
For, to find his Shangri-la, not only had he to traverse endless mountain ranges, but some of the deepest gorges in the world.
The Nujiang is called The Angry River.
This 300-kilometre stretch of raging rapids is as much a barrier to life as are the mountains above.