Into the Mournweald quest will start after you talk to Odo, in the Legions Chapterhouse. Mournweald is a forest, and Odo wants you to find Hugh Montbarrons signet ring which may open the Legion Causeways.
To begin your adventure, go to the central large hall inside the Chapterhouse, and then downstairs.
There is only one gate that can be opened open, but be careful, because if you destroy the spider eggs near the entrance, you will be attacked by spiders.
Open the two gates and you will enter the East Forest.
To the right is a quest, near a corpse. Its easy to spot, because it has a yellow exclamation mark. Approach it and you will receive A Loss of Words quest.
Quest: Enter the Mournweald
After you enter the East Forest, you will notice on your minimap that the starting area is divided. There are several small entrances and hidden passages.
These areas are inhabited by spiders and they attack in large packs. Make sure you kill each pack for additional gold and experience, and dont forget that the spiders are poisonous.
Advance but stick to the right part of the main road, because there is a passage which takes you to the Shadow Rift Cavern.
The passage is marked on your minimap by a green leaf (the saving point).
Quest: Hiding out
If you follow the road to the right, you will enter the Shadow Rift Cavern.
Use the save point to the left, then enter the cavern.
You are attacked by small spiders and some large black spiders will come down from the caverns ceiling.
Kill them and follow the tunnel. Make sure you destroy their eggs too.
Go down the first ramp and clear the next area, then go left and you will find the Manx Genealogy. Pick it up and go follow the corridor to the right.
Look around for corpses because they contain gold and special items. Loot them and then save your game, using the save point you see to the left.
Enter the large hall and you will hear Niku asking for your help. He is inside a cocoon. Approach the cocoon and press RB (on Xbox 360).
Talk to Niku and you will see the next boss you must kill: Palefang.
Palefang is similar to Vera, the necromancer, because he spawns small spiders and uses web-missiles to damage you. Killing Palefangs spiders first, is the only way to defeat him, otherwise you will be overwhelmed.
Dodge his web-missiles, and when he retreats to the other side of the room, follow him. Attack all the time and you will eventually defeat him.
After Palefang dies, talk to Niku again and set him free, to complete the Hiding Out quest.
Exit the cave and follow the path to the left of the main road, in the starting area.
Quest: Enter the Mournweald
Before entering the next area (see the save point on your minimap), make sure you are ready for a fight.
You will be attacked by a pack of wolves led by a forest man. While the wolves are easy to defeat, the forest man is tougher, especially because of his ranged attacks.
He throws rocks at you and you must avoid them at all costs, because the damage inflicted is huge.
Make sure you dodge all the time, because he also uses charged attacks.
Take him out and then take a look on your map.
There is an entrance to the left side of the road. Here you must defeat an Elder Dakkenweyr to get the Manx Genealogy. This boss is similar to the one described above, and as long as you dodge his attacks, you wont have any problems.
Enter his small settlement and pick up the Manx Genealogy and all items you find there, and then return where you defeated the first forest man.
Look on your minimap.
You will see two blue circles, marking two quest objectives.
Follow the road to the right and you will find a corpse, between two rocks. Loot him and you will pick up the Montbarron Genealogy.
Continue forward and you will reach a dead end. The path is blocked by roots.
Approach them and the roots will disappear.
Follow the only road you see, but pay attention to the corpses that can be looted.
Eventually, you will enter the Mournweald.
Quest: Find the Slained Legionnaires
Advance and you will notice that the enemies here are similar to the water-creatures you killed for Yacob.
Some of them will launch blue devices that affect specific areas. Dont stay in these areas, because you will take damage.
Kill them and move forward over the wooden bridge.
More enemies will appear on your way. Take them out and keep your eyes on the minimap, because on the left side of the main road is a small entrance, over another wooden bridge. Here you will find a Slain Legionnaire and several chests.
Investigate the area and return to the main path. Continue forward and cross two more bridges. Eventually, you will find the place where the last Legionnaires were killed.
Quest: Retrieve the Montbarron Signet Ring
Before picking up the Signet Ring, search the corpses for additional items.
After you take the ring, the Radiant Youth will appear. Talk to him and you will unlock the Sacred Meeting Trophy/Achievement. The Radiant Youth will also teleport you near the entrance.
Go back to the Legion Chapterhouse and in the large hall, return the books you found. A passage will open behind the library. Make sure you open the chest you find inside.
Talk to Odo an you will complete the Into the Mournweald quest. Your next quest is The Battle for Ravens Rill.