Circumventing the Druidic city of Mynelion is the Thicket - a dense part of the forest that's hard to get through. The tall coniferous trees stand closer together here than in other parts of the forest, and small bushes cover most of the ground.
Though it is possible to get through it with a little effort, the denseness of the forest isn't what makes it almost impossible to reach the city for outsiders - the trees themselves seem to move slightly, wandering slowly for a couple of inches before rooting themselves into a different spot. The constant sound of almost inaudible creaking whispers between the trunks.
In some spots around the perimeter there's not only trees. The space between the trees are overgrown with thick thorny bushes. If you have a valid reason to enter Mynelion, these bushes will simply pull back, giving you a clear path through. In every other case the bushes keep blocking the way through. If you try to get through, the bushes will grow denser and the thorns longer and sharper. The further you try to push through, the more likely it gets that you'll get stuck in the thorns, unable to move further, bleeding from a million small cuts. Your only choice is to turn around and leave. The thorny bushes will let you out.
What Kind of Vile Sorcery is This?
When the Druids established a teaching institution that would grow into the city of Mynelion they made sure the holy tree Akrimmon wouldn't be unhappy by their presence. As a token of this friendship the old hollow oak spread its magic through the trees surrounding the Druids' city. Not enough to awaken the trees completely, but just enough to make them able to move around. Akrimmon then gave the trees a sacred task - to protect the city of Mynelion against anyone who had no valid reason to be there.
The Druids are eternally thankful for this gift, and named their new line of defense after the natural phenomenon they felt it was the most similar to - the Thicket.