Yngol Barrow

Description
Yngol Barrow is an ice-filled tomb located northeast of Windhelm on the south side of the river bank. It contains Draugr and adept-level chests. The area also contains a puzzle door that requires the Coral Dragon Claw to open, which can be found either from Birna in Winterhold or within the barrow itself, located on a pedestal past a puzzle room. The final room contains Yngol's Shade, an undead wielding a honed ancient battleaxe, appears to use the frost voice, and may disarm. Upon defeating Yngol, the exit can be unlocked by removing the Helm of Yngol from the skeleton seated in the chair. Yngol Barrow is used for multiple quests, and the enemies within may vary depending upon which quests, if any, are active. Yngol's Shade may not always appear, instead being replaced by a Draugr Death Overlord or an unmasked Dragon Priest. The rest of the barrow may also be either filled with Draugr or completely empty before the final room.

As you explore around the interior of Yngol Barrow, you will encounter several eerie light orbs that are most likely sea-ghosts, the spirits which inadvertently caused Yngol's death. They will follow you around, but are completely harmless (although you can get trapped in tight spaces by them because they like to stand very close to you). They tweet lightly and roll from room to room often bouncing or coming out of holes and cracks in the wall and ceilings, before literally pouring out of the puzzle door. They will follow after the player even if no Draugr are awakened or present.


 * One possible explanation: The lights are Draugr spirits. Once you open the puzzle door, you will see several fly off, then hear the noise of the dead rising. However, this does not explain their presence if the final boss is the only enemy encounter.
 * Another theory: The lights are trapped spirits, lent credence by their disappearance after the player takes the Helm of Yngol, thereby breaking whatever spell had them bound there.
 * The most plausible theory is that the orbs are in fact Sea-Ghosts, who may have inadvertently led Ysgramor's son Yngol to his doom, according to the book Yngol And The Sea-Ghosts. The reason they remain in the Barrow with Yngol is known only to them (it may be to keep Yngol's spirit company, though it is unknown whether it is out of curiosity, or through remorse at inadvertently causing Yngol's death). They leave once the Dragonborn puts Yngol's spirit to rest and takes his Helm.

Pillar Puzzle
The player comes across a Dead Scholar and a pillar puzzle early in the dungeon. The scholar's corpse contains a book titled Notes on Yngol Barrow. It appears he had discovered the barrow in his travels and had been transcribing the Nordic carvings in the cave for the College of Winterhold. The notes provide the key to the Pillar Puzzle:

Activating the lever now opens the gate, revealing a Coral Dragon Claw on a pedestal. If you already obtained the claw from Winterhold, it will not be there. The Coral Claw is used to open the puzzle door and contains a clue to the sequence. Its order is (top to bottom) Snake, Wolf, Moth.

Quests

 * This is one of the possible locations in which the Helm of Winterhold may be found for the Miscellaneous quest initiated by Jarl Korir of Winterhold
 * The quest to find the Helm of Yngol
 * Dungeon quest: Ashore In A Sea Of Ghosts
 * A Location of the Ring of the Beast in Rings of Blood Magic
 * A Miscellaneous quest for Urag gro-shub in the College of Winterhold to find a book called 'REMANADA'

Notable Loot

 * There is a chest located under the bridge in the room with water following the pillar puzzle.
 * Chest and urns behind adept gate after second iron door.
 * The Coral Dragon Claw can be found in here.
 * There is a chest in front of the throne in the last room visible when you enter from the cave entrance.
 * Helm of Yngol.

Enemies
The following enemies appear depending on your active quest:
 * Draugr Death Lord or Dragon Priest (Retrieving the Helm of Winterhold)
 * Yngol Shade (Retrieving the Helm of Yngol)

Bugs

 * When entering the dungeon, the game screen may become black. While the navigation bar on the top will still work and the player can do all movements judging by the sound effects, it is impossible to access any menus but the system menu. Quitting the game from the system menu may cause the game to freeze, requiring a reboot of the system. The issue can be solved by entering the dungeon without a follower or by saving inside the barrow and loading from that save. (1.5)
 * If you enter Yngol Barrow with the quest of finding the Helm of Winterhold, after defeating Draugr Death Overlord and retrieving the quest item, the last gate will NOT open. This issue can be solved by simply exiting the crypt the way you came in.
 * There isn't much beyond this gate, besides a staircase leading directly to the exit and a chest containing a meager amount of loot, but if you encounter the above glitch and really want the stuff in the chest on the other side of said gate, you can always find the other entrance to the Barrow that isn't marked on your map. Entering from this side will put you in the barrow on the other side of the gate. To find this door, fast travel to the barrow. Head left, around the entrance's outcropping of rocks, and keep heading North-East up the hill, and then down again. Head all the way down to the waterfront, and look to your right. There should be a sizable outcropping of rock, at the base of which is the door leading to the opposite end of Yngol Barrow.
 * If you try to complete the Helm of Winterhold quest after completing the Imperial path for the Civil War you cannot give the helm to Korir as he will not talk to you.
 * When arriving at the gate with the pillar puzzle, all three of the pillars might be set to the hawk emblem, and they might not respond when using the "Activate" prompt. This can be fixed by re-entering the Barrow.
 * If you kill Yngol's shade by shooting through the last gate, having accessed it via the door on the surface, Yngol's skeleton and the helm might be invisible when you reach the final chamber coming from the front. All that you can see will be Yngol's skull hovering in the air above the throne chair. You will receive the prompt to take the helm, though. On doing this, the skeleton will reappear and the last gate will open.
 * When arriving at the dragon claw door it may not activate, thus leaving you locked out of the final room. The issue can be resolved by going to the home screen then restarting the game. You may find then that the door is now open.
 * When speaking to Dragon Priest], there's a chance that you may not be able to complete the quest. His dialogue freezes and the quest will remain within your Miscellaneous Quest listing.
 * Sometimes, the Dragon Claw will not insert into the door even though the sequence is correct. If you are doing the Trouble in Skyrim Quest for the Companions and only have to kill the Draugr Death Overlord, this can be solved by going in the back entrance and killing him with spells, but you may not be able to retrieve the Helmet.
 * A Dragon Priest may appear instead of Yngol. This prevents acquisition of Yngol's Helm and the unlocking of the rear exit. (Occurred during Rings of Blood Magic; caused by installation of Dawnguard?)
 * After killing Yngol's Shade, if you leave out the rear exit and re-enter, a searchable Dragon Priest-looking body may appear as the body of Yngol's Shade, in addition to the ash pile that was left when you killed it. Items placed in one will appear in the other, but stolen items won't show their stolen status, however they will still be stolen when you take them back. If you try to Dead Thrall the body, it will say "Dragon Priest resisted Dead Thrall".
 * I have fixed the black screen bug by casting candle light and working my way out.