I have been to Yumthang valley twice in 2014 and 2016 during my stay in North Sikkim. It is situated in Sikkim at a distance of approximately 76 km from Mangan, the district headquarter of North Sikkim and approximately 150 km from Gangtok, the capital of Sikkim. The ride is nearly 3 hrs from Mangan and nearly 6 hours from Gangtok. It is situated at an altitude of about 3564 metres.
It is a very picturesque place with its snow clad valleys and a variety of beautiful ground flowers. It also harbours different species of Rhododendron and mountain trees. We won't find any more trees above this level. The best time to visit is from last of March till first of May.
However the major obstacle is that the route is inconvenient since the road is not properly maintained. Also it is very risky to visit during the rainy season due to the frequent occurrence of landslides.
It is also difficult for the old people and underweight people to visit this place due to high altitude.