The length of a single round trip is 100 km, but it isn't as simple as that. They all remembered their first experience through the ordeal. For most trainees, this is the first time that they have encountered such an environment.
There are a lot of things that made them fail the first run. First is the unusual terrain. The terrain was unfavorable to them, the ground was not safe to step on as they wished. Going up and down the peaks made things very difficult. Next are the cold winds. The mountain range may be artificial but the conditions are real.
The cold numbs the flesh and the mind, it will make stumbling very easy. The eyes cannot be used because of the snowy wind, so the divine sense has to be turned on throughout. It is a good thing too because only the divine sense can warn you of unreliable grounds not to step on. But the range of the divine sense is too short at this stage which makes getting lost very easy.
