A further 40km north of Mangan lies CHUNGTHANG, set in a deep valley that sees little sunlight, a grubby town with a destructive hydro-electric project at the confluence of the Teesta and Lachung rivers. The road forks here with the one to the right climbing rapidly to the group of small settlements of LACHUNG, the “big pass”, a mere 15km west of Tibet. Across the river from the main cluster of settlement, Lachung Monastery is a two-storey Tibetan-style gompa belonging to the Nyingmapa sect worth visiting especially for its wonderful murals. The Bhotia people of Lachung and Lachen practise a unique social system known as Dzumsa – a sort of gathering of elders that controls everything from grazing rights to law and order. Accommodation here must be pre-booked along with all food and transport through tour operators such as Blue Sky, Galaxy and Khangri in Gangtok
As the road north ascends past yak pastures, it enters the Shingba Rhododendron Sanctuary announcing the start of Yumthang (3645m), 25km north of Lachung, with spectacular rock and ice pinnacles towering to 6000m on either side. This beautiful tree-lined valley does not have accommodation but boasts somewhat neglected hot sulphur springs. A pleasant purpose-made walking trail leads 10km along the valley floor, back to the sanctuary gates – due to the high altitude and problems with acclimatization, descent rather than ascent is recommended. Past Yumthang, the road continues up the valley and emerges on the high plateau land at Yumesamdong or Zero Point (the end of the road), at an altitude of 4770m.