Just visible across the river from the road between Lhasa and Shigatse is the Bönpo Yungdrungling Monastery. The monastery, founded in 1834, was once the second-most influential Bön monastic institution in Tibet and home to 700 monks. At first glance, Yungdrungling looks much like a Buddhist monastery, but if you look closely you'll note the swastikas and prayer wheels swirling anticlockwise. You may find your guide and driver are reluctant to enter the monastery grounds.
There are currently around 80 monks here, from all over Tibet. If one of them can find the key, you can visit the large dukhang (assembly hall), with its impressive thrones of the monastery’s two resident lamas. There are 1300 small iron statues of Tonpa Shenrab (the equivalent of Sakyamuni) along the walls. You may also be able to visit a couple of chapels beside the main hall, including the Namgyel Lhakhang and Kudung Lhakhang, the latter featuring the tomb of the monastery founder and Bön protector Gyachen Traksen. Remember to make the rounds in an anticlockwise direction.
The monastery is 80km east of Shigatse, on the road to Lhasa and the north bank of the Yarlung Tsangpo (Brahmaputra River), just east of where the Nangung-chu meets it. Cross the Bailey bridge and follow the dirt road (in the process of being paved at the time of writing) north along the Nangung-chu to a road bridge. The monastery is 7km from the main road.