Maps - Azeroth - Kalimdor - Mount Hyjal

Mount Hyjal is not under Kalimdor in the Achievements.
(It is part of the Cataclysm achievement)

The Rim of the World seems to be the ridge that goes around both sides of the Shrine of Aviana continuing West then South to Ashen Lake then Northwest from there to Lightning Ledge - hopefully crossing it anywhere in there will get you credit for it.

When you get far enough along in the Mount Hyjal quest chain The Flamewake becomes The Regrowth. We can only hope that a character can't get that far without getting credit for The Flamewake.