Translation:The weather is good. Let's go hiking!
"The weather is fine. Let's go hiking" would also be a correct translation. Reported on Nov. 19, 2017.
I believe 登山 is also a widely accepted translation for hiking. Whereas 爬山 connotes non-technical mountain climbing activities and 攀岩 would refer to technical rock climbing with ropes and harnesses and gear, etc. No? I think "Let's go mountain climbing should be accepted."
Hiking includes non-technical mountain climbing activities and 登山 is usually only for mountain climbing, actually.
I think they would use a stronger modifier (i.e. 非常) if they wanted to say "fantastic" over simply "good."