Vertical
In the mountains, they stand alone against whatever will happen. For the several days they live in nature, they can rely only on themselves and each other. Elsewhere, there is always a fallback - here one is without a safety. This in itself can bring some to terror - the terror of having to rely on yourself - your own judgment, wits and fortitude. This is also the most incredible feeling of strength and independence. Knowing there is no safety means having to be one's own safety.
