A major handicap of all expeditions to the north side of Mount Everest is the tight time window between the end of winter and the start of the monsoon rains. To travel from Darjeeling in northern India over Sikkim to Tibet, it was necessary to climb high, long snow-laden passes east of the Kangchenjunga area. After this first step, a long journey followed through the valley of the Arun River to the Rongbuk valley near the north face of Mt. Everest. Horses, donkeys, yaks, and dozens of local porters provided transport. The expeditions arrived at Mt. Everest in late April and only had until June before the monsoon began, allowing only six to eight weeks for altitude acclimatisation, setting up camps, and the actual climbing attempts.