You need the climb and swing ability to do this, go to the living forest. in the first area, near the save poin, there are two branches near the temple like thing. Grab the first one and jump to the second and jump towards the temple. You will then grab a tree coming out of it and climb up. You will then be in a new area thats just a jaged path with putrid corpses and masked guards. at the end youll come to an area with a purple portal. You'll fight Millena and two masked guards.