The surface of Feuerberg is irregular, mostly sloped, but occasionally breaking into great cliffs and chasms that rise and plunge dramatically. While much of the base is able to be walked or scrambled up, albeit slowly, the top halves of Feuerberg and Himmelberg are open almost exclusively to those who can drag themselves up steep cliff-faces.
Climbing the world's largest mountains happens at the scale of overland travel. Rather than focusing on every ledge and chimney, travel is abstracted across a hex grid where the hexes have a diameter of 1km, and it takes approximately 1 hour to traverse a hex (mostly due to changes in vertical height and stopping to rest so the party isn't too exhausted to fight). Because of the reduced scale, instead of the full overland travel procedure, a cut-down version is used.
For each hex on the mountainside, the caller must make three choices.
1) Are they looking for paths, or are they pressing overland?
By spending an hour and rolling 6+ on 1d6 the party finds a path, which is generated in an ordinary way. PCs can follow the path, which requires them to follow it as it meanders, or they can depart from it and lose its benefits to travel in another direction.
2) Stealthy or. Straightforward
Traversing a hex stealthily increases the chance of getting lost. While traversing the hex, the caller rolls 1d6. On a result of 3-, the party is lost and they fail to exit the hex. While travelling a path, the party is lost only on a result of 1.
Traversing it in a straightforward way increases the chance of random encounters. While traversing the hex, the guard rolls for a random encounter. On a path, the party can reroll one of the d6s.
3) Safety or Speed
Traversing a hex safely increases the time it takes. It takes 1d6+1 hours to traverse a hex safely. On a path, it takes 1d4 hours.
Traversing a hex speedily increases the risk of an accident. Everyone makes a saving throw. On a failure, they either destroy one item in their possession or they take 3d6 points of damage (PC's choice). On a path, they get +4 to their saves.
Weather and specific terrain types can alter this further, making certain days and places particularly good for stealth, etc.