Namcha Barwa, Mountain of Burning Thunder, still guards the heart of the world, as he was sent by the gods to do. As kings, he and his brother Gyala Peri watched over southeastern Tibet, a land of mystery to this day. But Namcha Barwa slew his brother in jealousy, decapitating him and throwing the head away. The gods turned them both into mountains, Namcha Barwa 7800 meters high, Gyala Peri and his missing dome 7300.

So sayeth the Epic of King Gesar, Tibet's ballad and the longest literary work in the world. No myth could fit better. The world's highest monument to guilt and jealousy, Namcha Barwa veils itself almost unceasingly in clouds and mist. On the rare days that the sun can burn away its cloak, the mountain astonishes in its stark beauty. Chinese National Geographic named it by vote China's most beautiful mountain in 2005, but such flattery does nothing to sway the silent sentinel. Namcha Barwa has defied all but one ascent to his peak, in 1992 no less, and still holds off all but the hardiest from reaching its charge, the enigmatic Yarlung Tsangpo Gorge.

The Yarlung Tsangpo River wends its way through 1700 kilometers of Himalayan headland. At the foot of Namcha Barwa, it takes a sharp turn south, and begins a course through 250 kilometers of gorge so deep and lush that the Grand Canyon is a dusty trench by comparison. At an average depth of 5000 meters, Yarlung Tsangpo Gorge provides a vertical tour of all the earth's ecosystems from rainforest to arctic, but only to the hardiest birds.

The river rages and churns to ensure that only it may traverse the gorge to its southern exit, where it emerges into India purified, becoming the sacred Brahmaputra. Kayaking expeditions have tried and failed to make it all the way through, with death attendant on audacity. A National Geographic expedition in 1998 lost expert kayaker Doug Gordon in the attempt, and it wasn't until 2002 that an international team completed a descent of the gorge's upper section.

But Yarlung Tsangpo Gorge is no glorified corridor to pass through on a dare - its hidden nature conceals treasures ecological and spiritual, long seducing outsiders who are only now getting glimpses. Chief among Yarlung Tsangpo's jewels are the Hidden Falls, a sacred site to Tibetan Buddhists, concealing a tunnel to a paradise realm, the Shangri-la that James Hilton erroneously located in Tibet's northwestern frontier. Three foreigners, led by native Monpa guides, reached the falls in 1998, but remain mum about any tunnels to Buddhist heaven on earth.

In fact, the falls' environs, covering a region of 3000 square kilometers, are holy in their own right. Pemako, in the heart of the gorge, is "hidden lotus-land", a physical manifestation of the Buddhist tenet that true beauty and happiness lie in concealment. A handful of Monpa and "true" Tibetans live there now, occupying a realm of rich virgin forest as far from the desiccated Potala as the imagination can roam. They are hardly indigenous, but benevolent trespassers who came from Tibet's Chamdo region a century or so back. If any tribe truly belongs to Yarlung Tsangpo Gorge, it is the Luopa, pygmy hunters all but unknown to ethnographical study.

And that's the true appeal of the gorge; it is all but unknown and looks likely to stay that way. Much life thrives there that would vanish on exposure, however well intended: leopards, tigers, bears and their prey -  takin, musk deer and the wild water buffalo. Other living things exist nowhere else but in the gorge, an astounding 350 new species documented over the past ten years and recently revealed in the World Wildlife Fund's report Where Worlds Collide. Flying frogs, a flower that changes color with temperature, and the world's oldest mushroom are but a few of the bio-finds made by the patient, intrepid researchers who have been making forays into Yarlung Tsangpo Gorge. Besides terrain that cars can't even get close to, they faced dangers like the king cobra, which regularly grows over two-meters long in the gorge's rich undergrowth.

Besides Namcha Barwa, cobras, and the implacable Yarlung Tsangpo River, the gorge has enjoyed the protection of the Chinese government, which long ago declared its end a national reserve off limits to all without express permission. The practical, predictable horror lies in the studies being done to assess the Gorge's feasibility as a major dam, one which would exceed the Three Gorges Dam in size and double its output. Such a dam would easily disrupt some 100 million lives, but mostly those on the Indian side of the gorge, which would of course become a memory. No verifiable word on if and when construction of the dam begins, only hope that the wrath of Namcha Barwa still commands respect.