As far as mountain climbing is concerned, consider this point.
You can move at normal speed all day, even if that "normal" is restricted by terrain.
You can move at double speed (Hustle) for quite a while before fatigue sets in.
You can run (quad-move) from one round per CON point before you need to start making dice rolls. For John Q. Public with a CON of 10 or 11, that's about a minute at a time.
By the rules though, you can rest for a short time, then run again.
Rules for fatigue from Hustle are based on hours of movement, not minutes. You take 1 subdual point after the first hour, 2 after the second, 4 after the third, and so forth, doubling the damage each hour.
So a healthy normal (i.e. 2nd level Commoner with 6 hit points) could Hustle for just under three hours at a time, and taking 3 points of damage (1 + 2). After that they rest for an hour, recovering two subdual points (one per hit dice), bringing them back up to 5 points. Then they can climb/hustle for an hour more, taking 4 of their 5 for this one.
They can also Run (speed-climb) for a minute at a time, safely, then rest for a minute and do it again.
They'd be able to do that all day long if it weren't for the rule in Overland Movement that says run/walk is treated as a Hustle when done over long distances. That means you go back to counting non-lethal damage on them for each hour.
For the casual rock climber, a 4 hour climbing day isn't a bad one. You're tired and a bit sore, but you're okay. Just remember to break for lunch.
And of course, there's always the option of walking/climbing slowly, moving 15 feet in a round as a "normal move" (30 feet being normal, cut in half for difficult terrain). You could do that for 8 hours, by the rules, without taking any non-lethal damage at all. It's just slow going.
