Re: tiring or amazing?
I have a totally different opinion about this.
Yes, "absolutely tiring" is not a normal combination, but that's not the point.
The writer is referring to the effect that the knowledge that people climb mountains has on him/her.
I do not get tired hearing that someone else ran a marathon.
It is tiring TO run a marathon.
It is not tiring TO ME to hear that people run a marathon.
I may be surprised to hear people enjoy running marathons, but I'm not tired to hear it.
Rewrite the original sentences as "It is absolutely ____ to me" instead of "I think it is absolutely ____" and this becomes even more clear.
It is absolutely surprising to me that
It is absolutely tiring to me that
It is absolutely unusual to me that
It is absolutely amazing to me that
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.