i actually want to post a bug report about this. but since i'm like the only person who run there (pickin chests, robyn stuff) and managed to loot 50 levels from it, that kinda lessen the bug credibility. hence i'm discussing about this bug here.
some (actually quite a lot) of the trees blocks the path, while it might appear wide enough to allow passage, and some even placed in a way to make it looks like a path but still doesn't allow passage. annoyingly, henchmen and mobs can actually go through. apparently, with some trial and errors, i found out that the only one who can squeeze through some of those wide-yet-narrow-path are Female Humans and Elfses and ONLY when they are equipped with either Mace or Warhammer.
of course, if your class has a teleport skill, this won't be a problem. but future Glimmering Forest explo(iter)rer might want to take a note of this.