The Yarlung Zangbo Grand Canyon is considered to be one of the longest and highest in the world; at its deepest, the valley between the peaks of Namjagbarwa and Jialabailei is over 7,000 meters (22,966 feet) deep. Following the course of the Yarlung Zangbo River, which becomes the Brahmaputra once it enters India, this canyon is one of the great spectacles on Earth for those fortunate enough to see it.
Accessed from a handful of small encampments along its length (Samye and Pei are both near some amazing stretches), hikers will have the opportunity to see an ecosystem that ranges from subtropical to Arctic as you climb in elevation. It may be best to explore the valley and the waterfalls that are plentiful here; climbing peaks such as Namcha Barwa (7,782 meters/25,531 feet) are going to be generally out of the question, except for the most experienced and prepared of climbers.
Driving from Lhasa takes about 6 hours, despite this canyon being so close on a map. The problem is that the road infrastructure is still largely undeveloped and the nearest route is still exceptionally roundabout. Don't let it deter you; this is a truly once-in-a-lifetime experience!
Note:The Yarlung Zangpo River itself, which is Tibet's most important river as it drains the Tibetan Plateau into the Indian Ocean, has been attempted by professional kayakers and never completed in full. Unfortunately, some have died trying, for the river has numerous Class V+ rapids, making it a death trap for even the heartiest adventurer. An opportunity to view this spectacle of nature from shore would be much safer and surely as satisfying. More here.