The Mountains of Madness
Finally, some four days later, you hike through the foothills to the base of the mountain. It towers over you, all sheer forbidding cliffs and bare stone faces. A narrow path starts up the mountain through the trees that cover its base, marked by stone cairns. Some of these cairns are large and elaborate, while others are just a few pebbles stacked atop each other. You quickly learn to watch for any stacked stones, because these markers are the only way to tell the actual path from countless game trails or false appearances of a path on the way up.
The trail gets harder to find, as you ascend. Voh'ren is put to the test, trying to find a safe path up fields of scree or through cracks between boulders. At one point, the path leads straight to the bottom of a cliff face, and you are forced to climb it or find your own way around. At another, you are required to jump from one boulder to the next with the reward of failure being a drop down to a loose slope of scree that would collapse into a rockslide if you fell.
Mount Callahan, it seems, deserved its reputation as a particularly hostile mountain. The climb is hellish. The air is thin, too thin, and you soon find yourselves gasping for breath that will not come, the air simply not rich enough to provide the life-sustaining energy you need. You are tired. Your head hurts.
Okay, in no particular order, you need the following.
1. Someone has to roll Survival to find the path. Three checks at DC 15.
2. Climb checks to get up the cliff face. If one person can make it, they can leave a rope. It takes three successful checks at DC 20. Failing the first does nothing, second does 2d6 falling damage, third does 4d6 falling damage.
2a. If nobody feels confident in a climb, you can roll Perception or Survival to find a route around. There might be one; there might not.
3. Acrobatics checks for the boulder hopping. It's only DC 12, and only one check, but the consequence for failure is pretty stiff. You can rope yourselves together, in which case the rest of the party can roll a Strength check to catch you if you fall - but if they fail, you're all tumbling down.
4. Fortitude saves for the altitude. DC is 15, 16, 17 for the three saves. Failing one causes you to be fatigued; a second or third failed save escalates that to exhausted and does 1 point of damage to each ability score. Any bonuses against high altitude or the like apply, as does the Endurance feat.