Siege on the Dragon Cult

Overview
At the approach to the entrance of Forelhost, Captain Valmir, who has set up camp outside in the courtyard, starts a conversation with the Dragonborn. He asks for help with retrieving a mask from inside the tomb. The mask he is referring to is the Dragon Priest Mask Rahgot. He also, as an optional task, asks them to find Skorm Snow-Strider's journal. Follow the captain to the entrance and the quest starts.

Note that killing Valmir upon meeting him incurs a bounty, but since nobody is around there is no penalty involved. Killing him when you meet him will neither fail nor start the quest, and the dragonborn will be free to explore Forelhost and keep the Priest Mask without penalty. When you get the mask you will receive a notification the Quest will have been completed, but it will not appear as a Journal Entry.

Objectives

 * Obtain Rahgot's Mask
 * (Optional) Find Skorm Snow-Strider's journal
 * ​Return to Captain Valmir
 * Kill impostor Captain Valmir

Captain Valmir
The Captain can be pickpocketed before entering to find Valmir's Orders (or they can be gotten at the end of the quest), and find out that Captain Valmir is an impostor. The orders read:

"You will proceed to the ruins of Forelhost to retrieve the Mask from the Dragon Cult there. If you are discovered, impersonate an officer. It is unlikely that anyone from Skyrim will be clever enough to see through the disguise. Once you have obtained the Mask, bring it to Labyrinthian."

Forelhost Stronghold
Enter and proceed into a large room with a dead Imperial and soon a Dragon Cultist will appear, ready for battle. Dispose of him and follow the marker and then turn right. Beware of traps on the floor and more Dragon Cultists who will appear along the way. Turn right again and go up the stairs, when passing a corridor on the right, a swinging blade trap will begin to move.

Inside the next room Skorm Snow-Strider's journal will be on a table. Pick it up after the two Dragon Cultists have been killed. Reading the journal will give a hint of what happened here a long time ago. Continue through the doors on the left and pass a large bedroom, walk to the left again through a door and enter a large area overlooking a room with another Dragon Cultist.

Proceed down the ramp, through the dining area and turn right into a room with a ramp where two draugrs, or draugr scourges are waiting in their coffins. After they are disposed of, walk up the ramp to get to the trapped chest.

Walk down the ramp and go through the door on the right into a corridor with burned corpses and then turn left. A leveled draugr will be waiting in front of the door to Forelhost Crypt.

Forelhost Crypt
Walk along the corridor and at the end is a way to the left with a cage and a locked door (master) and a swinging blade trap, further along a way to the right. Go the way to the right, pass a burial chamber before coming into a circular room leading into the crypt area where a large number of draugr of different levels await. There are also several traps on the way, such as floor plates, rigged chests, swinging axes, magical runes, and soul gems that shoot fire, frost or lightning.

Continue through the door on the right into a large room with several levels. Three leveled Draugrs will emerge from their coffins as soon as it is entered. The Forelhost Well Key mentioned in the journal is in the chest by the coffin. Walk back up the ramp and over the bridge, jump over the gap to get to the chest standing there before going higher up. Shoot down the soul gem trap if possible before passing and continue to the barred door that will lead to the circular room.

Go back through the circular room to the corridor where there was a way to the left with the swinging blade trap. Use the Well Key, or pick the lock on the cage (master), and walk down the circular stairs. The stairs ends under water, swim along the corridor to a large cave where there is one frostbite spider (dead) and a few skeevers. Continue to the right, again under water, into a room with a note on the table and a dead draugr. Go through the door, avoiding the pillar trap just inside. Leveled draugr(s) will awake as soon as the room is entered. Walk through another crypt with several dead draugr and enter Forelhost Refectory.

Forelhost Refectory
Walk up the stairs and face some more leveled draugr, and at the end of the short corridor are a pair of leveled gauntlets on a pedestal in front of a large carving on the wall. Removing them sets off a dart trap. Go back and through the iron door into a large room with tables, a gate and several draugr. On the table lies another note.

To access the balcony on the right side, go through the door on the left and follow the corridor and enter a room full of growing plants and a note with orders on the table. Three draugrs will emerge when the room is entered; defeat them and proceed up the stairs into an alchemy lab. On a throne you can find a dead draugr, who, according to the Alchemist's Note on her throne's handrail, is Head Alchemist Froda. It seems that Rahgot got her killed for her disobedience. Rahgot's Reply is beside a dead draugr on the throne. Go upstairs and to the right and enter the next room. Beware of a lightning soul gem trap when going in. On the right is the balcony seen from below where a draugr is waiting.

Disarm the trap with an arrow and continue round the corner into the library like room where the Glass Dragon Claw is on the right side. The spear-gate in the room will open when the claw is picked up. Continue through and open a wooden door to enter a room with an Arcane Enchanter, fight the enemies who emerge and leave to enter the Dragon Claw hallway. Activate the keyhole (fox, owl, snake(from top to bottom)) and walk up the stairs into the last chamber.

Final battle
When the Dragonborn reaches the top of the stairs, several draugr lords will emerge and the coffin containing Rahgot opens. (A [magic rune can be placed on the two coffins at the bottom of the stairs to draw out the Draugr inside.) When the battle starts, the dragon priest will rise and use his Dragon Priest Staff, likely a Wall of Fire. After defeating Rahgot and the draugr lords, pick up the Rahgot Mask, the staff and the Forelhost Ritual Chamber Key and go through the large door outside to the Word Wall to learn part of the Storm Call shout. Return to Captain Valmir.

End of Quest
Either jump down to the courtyard where the Captain is or go back through the tomb.

The Captain will be engaged in a conversation to either a Stormcloak or Imperial soldier (the opposite of the side chosen in the civil war, if not chosen yet then it depends on who was chosen in the beginning, Hadvar or Ralof) when getting close. Stumbling over his words, both men draw their swords and attack, as soon as Valmir is dead the quest is completed. Valmir's Orders, located in his inventory, explain that he was impersonating an officer and implies that he was hired by someone not from Skyrim.

Notable loot

 * Rahgot Dragon Priest mask
 * Dragon Priest Staff
 * The entire four-piece set of Ancient Nord Armor worn by the ghosts of the Dragon Cult, who appear as transparent draugr.
 * Ebony weapons (leveled)
 * Dragonscale Helmet

Mining

 * Gold Ore Vein
 * Quicksilver Ore Vein

Trivia

 * Captain Valmir will say, "Return to me once you've obtained the staff," even though the objective is to obtain Rahgot's mask.
 * One may obtain the word wall without fighting through the tomb.
 * Once you recieve the quest, stand at the camp; you can see the word wall directly at southwest, then head southeast and walk along the edge of the tomb wall, at the end climb up the rocks and turn over, and then jump over to the balcony.  However, you cannot enter the door from the balcony.