I've been following a purity route guide, and it is saying in the easter forest of runes to "Pick up items around the area before sneaking past the tree and entering the hidden tunnel with the red slime". I've been searching for a couple hours now, and I can't figure out how to find it. At first I thought it didn't exist any more, but it looks like there is an area in the north I reach somehow, maybe? Does anyone know where the hidden tunnel is?
When you first enter the eastern forest, there's 3 main paths: one up north, with the blue ether crystal, one a little south of where you enter, and one way down south at the bottom of the map.