In order to enter, you must have accepted the quest to kill Dread Horn from one of the elves in Heartwood. The Twisted Weald at first seems like a nice and quiet valley in the mountains with a few harmless pixies flying around. However, when you move in further you will soon discover that this place is nowhere near nice.
On the island in the small lake the creature known as Dread Horn can be found, before you can meet him you will have to gather six keys from specific creatures in the area.
Feral Treefellows, Raging Grizzly Bears, and Twaulo of the Glade will only appear via the Champion altar.
ChampionsTwaulo of the Glade
TeleportersTo Mushroom Caves