Waking Nightmare

Background
"I've overheard two citizens of Dawnstar complaining about horrible nightmares. They seem to be relying on a priest of Mara named Erandur for assistance. Erandur has assured me he can end the nightmares, the source of which seems to be within Nightcaller Temple, a place of worship for Vaermina. I have agreed to assist him in this endeavor and we are now on our way."

- The Dragonborn

Walkthrough
This quest is given to you when you visit the Hold of Dawnstar and speak to Erandur, who is in the Windpeak Inn. All the townsfolk are suffering the same nightmares and Erandur knows how to get rid of them. He wants you to travel with him to Nightcaller Temple, which is just a short distance east of Dawnstar, to stop the nightmares.

Upon entering, Erandur will need to cast a spell upon the wall to proceed. In the next room you will face Invader Orcs, which vary in strength according to your level. When you reach the barrier, Erandur reveals himself as a former priest of Vaermina who ran away during a long-ago attack on the Temple by vengeful Orcs. He became a priest of Mara and now wishes to resolve loose ends in the Temple.

In order to pass through the barrier you will need to go to the Library to find the book The Dreamstride. Along the way and inside the Library, you will face Vaermina Devotees. Upon locating the book, Erandur informs you that there is a way to pass the barrier, but it requires Vaermina's Torpor, a potion that allows you to re-live the memories of another.

Your next stop will be the Laboratory, where Vaermina's Torpor should be stored. There are some more Invader Orcs and Vaermina Devotees that will need to be dealt with as you go along. When Vaermina's Torpor is located, Erandur instructs you to drink it and upon doing so, you become Casimir, a Vaermina Devotee during the Orc raid on the temple. You are instructed to release the Miasma to protect the Skull.

After releasing the Miasma, you will find yourself on the other side of the barrier, where you must collect the Soul Gem powering the barrier. Erandur remarks about what happened, and then you proceed to the inner sanctum.

As you approach the inner sanctum, the two Vaermina Devotees that told Casimir (you) to release the Miasma come out and after some short dialogue revealing Erandur to be Casimir, they become hostile. After the battle, Erandur casts a spell to destroy the Skull of Corruption.

Here you can kill Erandur as Vaermina commands and take the Skull for yourself, or let him complete his spell to destroy the Skull. In the latter case, he can be hired as a companion for no charge. If you kill Erandur you get the following Daedric artifact:


 * Detailed video walkthrough
 * Skull of Corruption (Skyrim)

Notable Loot

 * There is a large amount of Alchemy Ingredients (including 2 daedra hearts) that can be found in the Laboratory.
 * Most of the Vaermina Devotees carry Alchemy Ingredients as well.
 * In the Laboratory, there is the Skill Book Mannimarco, King of Worms.
 * There is an expert level chest behind a wooden door in the Library.
 * In the final room, there is a treasure chest on the right hand side of the stairs leading to the skull.

Bugs

 * There is a glitch associated with this quest (confirmed on Xbox 360, PS3 and PC) where Erandur disappears when he enters Nightcaller Temple.
 * One possible solution (confirmed solution for PS3 and Xbox 360) is to speak to Erandur a second time outside the Temple temple before he manages to enter, then wait for 5 seconds before entering yourself. If nothing happens, Erandur might be back at the inn.
 * On PC, if the above doesn't work, there is a fix which will reset the NPC bringing him back to you. This will reset his pathing and since the quest is mainly following and escorting him should clear up many bugs. In the console (accessed by hitting the key to the left of 1 and above Tab, which is labeled as ~ on most keyboards) enter, then  . Note that using the console will disable achievements until the game is restarted.
 * Fix Waking Nightmare / Erandur Quest Bug (YouTube)
 * It may also be possible to fix the bug by waiting for 72-110 game hours, after which he might reappear at the inn. However, the glitch might reoccur when reentering Nightcaller Temple, so saving before either you or Erandur reenter is advisable.
 * To deactivate the barrier, the player must remove the soul gem inside the sparking basket next to the pull chain. (This is less a bug and more an aspect of the fact that you have to be pointing at exactly the right pixel in order to interact with, or even notice, an object.)
 * After the deactivating the barrier and clearing the first 2 rooms, Erandur may run ahead and wait for the player in the final chamber to complete the quest. In doing so, he will trigger enemies on the way that will then look and wait for the player in the rooms he passes through. It is also possible for Erandur to disappear making the quest impossible to complete.
 * After waking up, the barrier must still be removed. If however the player waits for a significant length of time and kills all the enemies until the skull is reached, suddenly Erandur will run towards and past you, away from the skull only saying you've got to hurry. He'll eventually disappear and after removing the barrier another Erandur will still follow you, triggering the final battle.
 * Sometimes, the player can talk to the enemies before they awaken. They will say something, then "awaken" in a hostile state. (PS3 and Xbox 360 Confirmed)
 * After the last fight, just before reaching the skull of corruption, Erandur will offer no dialog options.(PS3 and PC Confirmed) It is possible that reseting his location to the player will resolve this issue (open the console and type  and then  ).