Where I normally put my translation attempt
I understand this bit:
The Alps' highest peak, Mont Blanc, which has high popularity among climbers throughout the world
although I'm a little uncomfortable with joining 最高峰 and モンブラン. I feel there ought to be a という in there somewhere.
But I can't understand the overall structure of the sentence at all. I think it should be of the form Aは/がBだ, but there doesn't seem to be a topic/subject to go in the A position.
Perhaps it doesn't help that I have no idea what 日本をはじめ means. Literally "something started Japan and ...".
Edit: maybe A = 日本をはじめ世界中の登山家の間で人気が高いアルプス山脈の最高峰 and B = モンブラン
I guess that would make sense, but is it really okay to miss a particle here? And even then I still don't understand 日本をはじめ