BRECILLIAN RUINS
The spirit the Warden encounters in the ruins reveals that humans had built the structure long ago. Curiously enough, it was an elven sanctuary where, according to the presence, "the eldest came to slumber", and others came to pay tribute to the gods on their behalf, explaining the presence of altars, tombs and gravestones found in the ruins. It is therefore implied that humans were coexisting with the elves in some form.
The structure and its inhabitants, human and elf, were destroyed by a "terrible presence", though exactly what that presence was had been forgotten by the arcane warrior's spirit over time.
Walkthrough
The ruins in the Brecilian Forest include two levels leading to the werewolves' lair.
Note: Leaving the area or entering the ruins will trigger the spawning of new enemies in the forest behind you; the first time you return or leave the ruins the Warden will face a large group of darkspawn (hurlocks and genlock alphas).
Ruins Upper Level
The Warden enters this level from the eastern corridor (Brecilian Forest Upper Ruins Map, L1), in a large room where a couple of werewolves give the party their own brand of welcome. The stairs leading down and north-ward from this room lead to the Lair of the Werewolves, the Warden's objective. Unfortunately, the door is barred and to reach the lair the Warden will have to travel the long way through both the upper and lower level of the ruins to find a second entrance (your quest log will update, telling you that you need to find an alternative path).
Note: * The Upper Ruins have 3 secret doors. They look like bricked-up arches, but once the controlled party member gets close enough, they are recognized for what they are. Loot and enemies are found behind the doors, and sometimes multiple doors are connected so that opening one will open a second door (behind the party).
The doors are located just prior to reaching the downward staircase and tree roots.
The two secret doors are found on either side immediately upon entering the Upper Ruins. A locked chest is located through the left-side secret door, looting it yields a letter needed for the Correspondence Interruptus side quest (Brecilian Forest Upper Ruins Map, L2)
The third secret door is on the left side of the large room just after the stairwell and tree roots.
There are multiple traps located throughout the ruins, it is recommended to have a rogue up front in order to detect them.
The only way is beyond the door facing west, where the Warden will meet giant spiders and Web Traps. Straight ahead, and to the north the Warden will find a couple of small rooms with columns, some Piles of Rubble and Cocoons. The party should follow the south branch, which leads downstairs. As you descend, you'll hear the sound of a large creature in the distance, along with an auto-save, as well as nervous comments by your companions. At the bottom you'll enter a larger room with a few corpses lying around and a round mosaic in the center (Brecilian Forest Upper Ruins Map, L3). There are a number of traps surrounding the mosaic. When you cross the mosaic, a Dragon will swoop down and attack. If the party includes a character that can disable traps, some of them can be disarmed before starting the fight with the Dragon.
Note: * There are four (4x) invisible square pressure plates on the mosaic and two (2x) more around it, and when stepped upon, these traps will unleash fireballs.
If you avoid the mosaic and cross the room up against the north or south wall then the Dragon will not appear. You can still raid the Dragon Hoard.
The Dragon may drop a generic armor chest piece. The corpses, chests, and the Dragon Hoard in the room will make up for it. The Hoard will yield Falon'Din's Reach longbow (unlocking Codex entry: Falon'Din: Friend of the Dead, the Guide) and a Silver Medallion, along with a large selection of gems, potions, and gold. At the end lies the stairs (Brecilian Forest Upper Ruins Map, L4) to the Lower Ruins.
Lower Ruins
The Warden enters this level from the northern path (Brecilian Forest Lower Ruins Map, L1) in the middle of the map. The first thing the companions are likely to notice is a ghostly elf just ahead of the group. The spirit will move away as the party approaches, but a group of undead (skeletons and corpses) will raise up and attack. The two side rooms just ahead hold more skeletons, and the passage beyond that (just before the collapsed portion) contains web traps and more spiders.
The collapsed corridor will force the Warden to a detour eastward, leading to a larger room with a round mosaic in the center. After encountering a ghostly boy, a large group of skeletons will ambush the companions here. Check the south side room (Brecilian Forest Lower Ruins Map, L3) for a sarcophagus that yields a Fancy Scroll and a Carved Elven Tablet.
Note: As the party enters the larger room, the spirit of a young elvish boy will be walking around the mosaic, apparently looking for his mother. This spirit is linked to The Mage's Treasure quest; the Tablet found in the sarcophagus nearby is also linked to a sub-quest, The Elven Ritual, which will be added to the quest journal when picked up (to finish both quests you would need to go to (Brecilian Forest Lower Ruins Map, L4)
The group should continue east, and turn southward at the end of the corridor (or northward to complete The Elven Ritual and subsequently The Mage's Treasure quests). A group of skeletons will be waiting at the bottom of a flight of stairs. Once the group is defeated, a larger group of skeletons will spawn around the party.
Note: The room at the bottom of these stairs holds a Phylactery and a Broken Stone Altar (Brecilian Forest Lower Ruins Map, L11), both related to the Unlocking of the Arcane Warrior specialization.
At the next crossing, the party will meet 2 groups of undead (one from the side room to the east, the other from the corridor up ahead), while a third group waits behind the closed door to the West. The main path lies beyond that door.
Note: The southbound stairs lead to a small room with a Glass Phylactery linked to The Black Vials quest (Brecilian Forest Lower Ruins Map, L5)
Approach this door with care, since the large room (Brecilian Forest Lower Ruins Map, L6) behind holds many enemies (mostly skeletons), and a very large amount of traps (5 Pressure Plates surround you as soon as you step through the door, just to get you started). Keep the group from entering the door, and pull the skeletons to you (they have archers so you may have to run behind a corner to force them closer, or close the door after getting their attention). If the party can disarm traps, do so between pulling groups; otherwise walk carefully each party member past the door and hugging the wall. A stealth rogue with Combat Stealth can scout ahead and disable all the plates. A mage with area of effect or missile defense spells would be effective here. The skeleton groups and traps don't stop right past the door, so keep an eye on the movement of your companions.
Note: In the southern wing of the room, the Warden can inspect an Adventurer's Corpse to find an Adventurer's Journal associated with the Unbound side quest
Once the room is disarmed and skeletons are eliminated, the party can move through the door on the west side, into the corridor that was beyond the collapsed section at the beginning of the level. When it's relatively save for the rest of the team to show up order everyone to head west. Enter yet another large room (Brecilian Forest Lower Ruins Map, L7) and start off by eliminating closest targets. It would be a good idea to save your progress before using the stairs. Once the initial groups are dealt with, the party can descend the first flight of stairs into this enormous room (Brecilian Forest Lower Ruins Map, L8). Don't let the statues and paraphernalia distract you, because an arcane horror will spawn as soon as the Warden gets close enough.
The arcane horror will teleport from one corner of the room to another at regular intervals if someone tries to attack it at melee, making the fight difficult. At the same time, a large number of skeletons from the surrounding balconies and ancillary passages will pour into the room and attack the party.
It's often safest to attack the arcane horror with ranged weapons from atop the stairs. It will only counter with Spirit Blast against ranged attackers; or not at all if you have a long enough range weapon (e.g., range 50+ staff), stand on the stairs, and leave the arcane horror in the corner where it first appears.
The skeletons will eventually wander into the large room after a time if you remain atop the stairs.
You can remove its ability to teleport by having a party member stand on each of the 4 pads at the same time.
The arcane horror will drop a pair of Ashen Gloves among other things. More loot can be found down the flight of stairs facing south from this room (a sarcophagus holds Ancient Elven Armor unlocking Codex entry: Ancient Elven Armor and a Legacy White Shear). One of the chests has a lock difficulty of Very Hard (60 XP)—it can be opened if you have a character with Device Mastery technique and at least 24 points of cunning—it doesn't contain important loot though, thus it isn't a big loss if you can't open it.
A few more skeletons await the Warden on the path heading north from this room, but the entrance to the Werewolf Lair is just past them.