Oblivion:Dagon Shrine

Quick Walkthrough
# Travel to the secret Mythic Dawn shrine in Lake Arrius Caverns.
# Steal the Mysterium Xarxes.
# Return to Martin in the Great Hall of Cloud Ruler Temple.

Detailed Walkthrough
Travel to the Shrine
You've finally been able to track down the location of Mythic Dawn's secret shrine to Mehrunes Dagon. The location, marked on your map, is in the northeastern part of the province at Lake Arrius Caverns, just north of Cheydinhal. Unlike Weynon Priory and Kvatch, you cannot immediately fast travel to Lake Arrius unless you happen to have been there before.

Gaining Entry
thumb|right|Strict rules apply to your attire
The Doorkeeper just inside the cavern will let you into the shrine without too much hassle. He says you should go and speak with Harrow, Warden of the Shrine of Dagon. Harrow will ask you to hand over all of your possessions (including all of your gold) and put on an Initiate's robe. If you refuse, you'll get a warning and another chance to don the robe. If you follow Harrow's instructions, you temporarily become a member of the Mythic Dawn and you are allowed to follow Harrow into the shrine.

At any point, you can refuse to co-operate and instead fight your way in. You will be told that your cover has been blown. You will then need to fight your way through the entire shrine, killing all the cultists you meet. You can choose whatever option is better suited to your strengths. If you are stealthy - or just really good at running - playing along with the Cult may be advantageous. Strong fighters may have an easier time simply marching in fully armed and cutting down everything in their path.

There are a few strategies for coping with Harrow taking all your equipment:
Harrow will not take any quest items that you may have in your inventory. Therefore having weapons such as the Blade of Woe, Umbra, the Honorblade of Chorrol, or even the weapons shipment from The Desolate Mine can be advantageous.
You can drop most of your equipment on the ground just before speaking to Harrow (you may not want to drop small, difficult-to-find items like keys). You can then pick everything up the moment after you agree to hand everything over. This allows you to enter the next section fully equipped without blowing your cover. You will still need to loot Harrow later in order to retrieve your gold and any other items you allowed him to take.
You can subsequently pickpocket Harrow to retrieve some items. Zero-weight permanent bound items are perfect candidates, since detection is influenced by item weight.
You can obtain some replacement equipment from the storage room at the far end of the Shrine Antechamber. You should drop a few lockpicks before speaking to Harrow (and pick them up after you give him your equipment) because this room is locked. Even if you do not give your equipment to Harrow, a visit here is recommended because it has some nice loot.
You can also walk up to Harrow and let him see you. Then when he starts walking towards you, start walking backwards and back out the door. He will stop at the entrance to the door and start walking back to his position. While he is walking back you can go around him and go through the door without having to give up your stuff.
If you have a high conjuration level, one strategy that involves killing the doorkeeper would be to conjure up a spell casting creature (preferably a powerful one such as a gloom wraith or Lich) and, after having spoken to the doorkeeper, start attacking your conjured creature. Once it has become aggressive and attempts to attack you with ranged spells, immediately run and stand behind the doorkeeper and wait for a spell to hit him. Once he's been hit, he will immediately turn on your creature and begin attacking it, which will then make the creature target him instead of you. As he is not a particularly powerful NPC, the doorkeeper will likely perish relatively quickly; if he doesn't die on the first attempt, repeat this strategy until he does. Once he's died, simply move all of your possessions onto his body. Once you've talked to Harrow, go back and retrieve your items from his corpse, then proceed with Harrow to the Shrine. This strategy should make the battle at the shrine much easier.

The Ritual
thumb|right|"Hear now the words of Lord Dagon."
There are two main options here, largely dictated by whether or not you turned over your equipment when you entered the shrine.

If You Handed Over Your Equipment
Harrow will lead you to a ceremony, which is already in progress, directed by Mankar Camoran himself. After a short speech, Mankar will disappear into a magical portal to Paradise, his realm; unfortunately he will also take the Amulet of Kings with him. It is impossible to kill Mankar at this point, because he is flagged as essential. If attacked, he will become a "ghost", meaning that you cannot interact with him in any way (including attempting to pickpocket the Amulet of Kings, which is impossible anyway because he is wearing it). Trying to obstruct the quest at this stage can lead to a serious bug later, so your only option is to allow Mankar to escape.

Once Mankar gets away, a quest message will pop up to inform you that your new target should be the Mysterium Xarxes, because it may aid you and Martin in retrieving the Amulet. At this point you will be introduced as a new Initiate to Ruma Camoran, Mankar's daughter and she will ask you to perform a ritual sacrifice of Jeelius, an Argonian priest. You may choose to agree or refuse to perform it. If you refuse, the cultists will immediately turn on you. Since you are weaponless and vastly outnumbered, this will be a very difficult battle. You have several choices at this point:

Once you have the knife for the ceremony, you can wander around unbothered until you find Harrow among the worshippers. Simply use the dagger to kill him, then search the body for your items.
Kill Jeelius, which will allow you to wait until things cool off a bit before stealing the book. Although you are now part of the Mythic Dawn, you cannot get out of the cave until you take the Mysterium Xarxes. Wait for one hour, which will allow the whole room to clear out except for Harrow, Ruma Camoran, and one additional guard (who stands behind the altar area). Then proceed to grab the book, attack those three and escape, fighting any other cultists along the way.
Agree to the sacrifice (for now at least). Go to the podium and pick up the silver dagger. Then grab the Mysterium Xarxes and run for it. You'll need to keep running all the way through the Shrine Living Quarters (avoiding many cultists along the way). You won't be safe until you make it out of the caverns.
If you are powerful enough to deal with the cultists, you can refuse to make the sacrifice, or even free Jeelius.
If you want to save Jeelius, note that picking up the Mysterium Xarxes will cause the statue of Dagon to collapse on top of him. See Jeelius for tips on how to help him survive.
See Fighting the Cultists for tips on how to survive the ensuing fight.
If your sneak skill is high enough, you can pickpocket your best items from Harrow and then use those items to kill him and take the rest of your stuff back, making the rest of the battle easier.
Another way is to pickpocket some lockpicks from Harrow and use them to open the door at the end of the hall outside the Shrine. You will find a basement with some scrolls, potions and weapons which will make it a lot easier when you attack.

If You Blew Your Cover
If you refused to turn over your equipment in the first place, you will need to kill Harrow (and the doorkeeper if he runs in). Fight and sneak your way through the antechamber and into the main Dagon Shrine, where the ceremony led by Mankar Camoran is going on. Your quest should update with your new target: the Mysterium Xarxes. Fight your way to it. Taking it will collapse the statue, close the entrance and open a new exit through the cult's living quarters. Using this method allows you to take followers into the shrine with you.

Fighting the Cultists
In most cases, you will end up having to fight your way through many Mythic Dawn cultists.
By choosing opportune times to start fighting, you can reduce the number of cultists you will need to fight. In particular, most of the cultists will leave the shrine area if you wait for a while (the shadows on the upper level of the shrine area are good areas to hide while waiting).
If you are outnumbered by cultists at the shrine, you can stand under the statue of Mehrunes Dagon. When the cultists are under it with you, run and grab the Mysterium Xarxes. This will cause the statue to collapse on top of them, killing most of them instantly.
To avoid being cornered by multiple cultists, keep moving at all times.
Use area-effect staves/spells to damage as many people at once as possible.
If your conjuration is at least at an apprentice level, you can summon some bound armor and a bound weapon for extra protection against the cultists, as well as a summoned daedra or undead creature to help fight them.
If you're playing as a stealthy archer, you can sneak to the far upper-right corner and play sniper from a perch. It will take a significant amount of time for the cultists to run all the way around and up to reach you. You could potentially pick many of them off with poisoned arrows by the time they realize what's going on and begin to move in.
If you sneak up undetected on a cultist and cast a Frenzy spell, they will begin attacking each other. This can make it significantly easier on you because, as you never attacked directly, your cover will not be blown and one or more cultists will end up dead in the fight.
Kill Harrow first and loot his corpse for your equipment, which will make it easier to kill the other cultists.

Jeelius
Helping Jeelius to survive this quest can be challenging (although optional).

One challenge is avoiding his death when the statue of Mehrunes Dagon collapses on top of him. If you free him before taking the Mysterium Xarxes then the statue will not collapse on top of him: however, you cannot access the Living Quarters until you have the book, so this option makes it impossible to purge that area before he gets there. Otherwise, as soon as you grab the book, you can rush to stand over Jeelius, deflecting some of the statue, and casting protection and healing spells on him when necessary. Similarly, casting a short duration custom spell on him combining shield, fortify endurance, and fortify health can make him tough enough to survive the statue falling. Also, casting a destruction spell with an area effect on the falling statue may deflect most large chunks. Alternatively, cast Chameleon on self and Invisibility on the Argonian. Free him and he will run away, hiding in some corner. Now grab the book and the statue will collapse on the empty altar. Another method to easily keep Jeelius alive is by waiting in one hour increments repeatedly while the statue is crumbling on top of him. His health will refill each time you wait.

As soon as you free Jeelius, he will run towards the exit, avoiding as many guards as he can. However, he will always take the long path through the Living Quarters, even if the (much shorter) route via the Antechamber is still accessible. Jeelius is able to cast a few randomly-determined spells, so he might be able to heal himself and should be able to attack the cultists with a destruction spell. However, he will die if he gets cornered. Trying to follow Jeelius can make things worse because it just attracts more cultists than if he tries to flee alone. If you do try to follow Jeelius, be prepared to use many healing (or even defensive) spells on him.

To guarantee Jeelius's survival, you can delay freeing him until after you have gone through all of the Living Quarters and killed all of the cultists. Then return to the shrine, release him, and accompany him out through the empty corridors. This may take several attempts due to the statue falling.

If you escort Jeelius through the caves, he will thank you once you get outside and introduce himself as Jeelius from the Temple of the One in the Imperial City. If he survives, you can go to the Temple Of the One a few days later and he will give you free one-point skill boosts in Alchemy, Mysticism, and Restoration, provided they are below 90.

Escaping from the Caverns
No matter which option you choose, you will end up leaving the Dagon Shrine area through the door on the north side of the shrine, leading to the Shrine Living Quarters. This door does not unlock until you take the Mysterium Xarxes, at which point the door you entered through also locks.

There are many cultists (as many as 15) in the living quarters, all of whom have to be killed or avoided to make it out. Taking the time to check the chests and other containers can be worthwhile, because they may contain good loot but if taken, they are considered 'stolen' even though there is no 'red-handed' indication.

Once you make it through to the first zone, Lake Arrius Caverns, your way is blocked by a "Rock Wall". The turn handle to activate the Rock Wall is located at the start of the tunnel, in the same room.

Return to the Temple
When you finally make it outside, head towards Cloud Ruler Temple with the Mysterium Xarxes. Martin may be found in the Great Hall of the Temple, and he will take the Mysterium Xarxes. He believes it may hold the key to opening a portal to find Camoran, but he will need some time to safely study it.

Alternative Scenarios
There are a few less common options that you may choose to use to get through this quest.

Stashing Your Equipment
If you want to avoid giving your equipment to Harrow without dropping everything on the ground, you need to create a container where you can stash everything. This is possible if you are not averse to killing a follower and have obtained one who you are willing to sacrifice. Kill the follower just before talking to Harrow and place all your items in the body. Talk to Harrow, then go back and get your items. The advantage of this method is that if you have a large number of items (especially small ones, like keys), you can simply "take all", rather than trying to drop then find everything. One method for this is if you completed the Mages Guild questline, and have the Staff of Worms. You can reanimate a dead NPC and get them to follow you in. The Risen Flesh spell from the Shivering Isles quest The Hill of Suicides works just as well.

You may be able to get a creature to follow you in, instead of using a follower. Lure a bandit or troll (mountain lions won't go through doors) from the nearby Wind Range Camp (slightly southeast) to the front of the cave. Run in, and kill them inside - the Doorkeeper will even help you!

Sneak into the Antechamber
For fast and sneaky types at high levels, it is possible to sneak into the Antechamber without giving up your equipment or blowing your cover.

Talk to the doorman and have him open the door to meet Harrow. Switch into sneak mode. As you pass the doorman on your way down the hallway he is triggered to harmlessly rattle off something. Harrow will be walking towards you as you head down the hallway; making eye contact in proximity will trigger the dialogue sequence. Immediately retreat back to the antechamber while remaining in sneak mode - if he gets too close, he will launch the conversation you are trying to avoid. Harrow will follow near the doorman to a point, then turn around. With his back to you, sprint (still sneaking) past him, open the door, and - still in possession of all your weapons and items - head to the main chamber where Camoran is giving his sermon.

Always in sneak mode (Chameleon helps too), wait for Camoran to finish his sermon and enter the gate. Harrow enters the chamber and assumes the same position as if you had agreed to give him all your equipment. The sequence plays out as if you joined the Mythic Dawn, without the alarms that are raised by all the killings required for the "You Blew Your Cover" option. After Camoran leaves, Harrow will track you down as per the script - avoid him! Eventually Ruma Camoran will also nonchalantly pursue, looking to get your thoughts on killing the lizard. Lure them both to the elevated position next to the door you originally entered and kill them. This goes unnoticed by the other followers who then file past through the door you entered as if everything went as planned; leaving you in the main chamber with all your equipment and an undisturbed Jeelius and Mysterium Xarxes! From here the story varies, but the eventual outcome is that you kill everyone, collect the loot and free Jeelius.

In this scenario, it is possible for the Mythic Dawn agents in the shrine room to become hostile if you kill Ruma, even if there is no way they could have seen you. This does not happen if you kill Harrow. A way around this is to lead both Ruma and Harrow to a secluded ledge and kill Harrow from afar first, preferably in one hit while in sneak mode, so he does not initiate his dialogue. Then if you allow Ruma to come to you, she will not talk with you, but go hostile when she gets within talking distance after the death of her fellow cultist. If you kill Ruma after she becomes hostile, the Mythic Dawn agents will continue to act as if nothing has happened.

Easy Alternative for Sneaky Characters
Follow the script until Ruma asks you to sacrifice Jeelius, the Argonian. Agree for now. Pick up the silver dagger near Jeelius, taking care not to pick up the Mysterium Xarxes which lies nearby. Now instead of killing Jeelius, go into sneak mode and head towards the shadows at the far end of the hall in front of the statue. Harrow follows but as you are in sneak mode, he doesn't see you. Make sure that he is also standing in the shadows then sneak towards him and kill him. Just make sure that you kill him in a single strike, otherwise a battle will commence.

Recover your equipment from him and then wait for some time. Six or seven Mythic Dawn agents will leave the chamber. After they have left, stealthily take care of the remaining guards in the chamber and then attack Ruma. Grab the Mysterium Xarxes and make a silent retreat through the living quarters.

Notes
The front cover of Oblivions game box is also the cover of the Mysterium Xarxes.
Followers who accompany you into the caverns will kill the Mythic Dawn members for you, preventing you from having to blow your cover up until the point when you have to pick up the Mysterium Xarxes.
After your escape from the shrine, Mythic Dawn agents will now attack you on sight (due to a scripted faction-wide disposition decrease when you pick up the Mysterium Xarxes). Some agents are posing as townsfolk. Your only warning will be a scream, "For Lord Dagon!", before they summon their Daedric armor and attack you in the street. However, it is usually easy enough to find a guard to cut them down for you, and the townsfolk will help as well.
When you complete this quest, the Oblivion crisis escalates:
The chances that a random Oblivion Gate will appear reach the maximum level at any point during the game: the number of possible random gates increases to 50 (from 25), and the chance of a gate opening when you enter its cell increases to 50% (from 25%).
Seven fixed gates open, one outside of each city (except Kvatch and the Imperial City). These gates are part of the Allies for Bruma quest. When asked about their city, NPCs will mention the Oblivion Gate outside their walls.
A fixed gate also opens near Fort Sutch, which is part of the non-journal quest Attack on Fort Sutch.
The only Oblivion Gates that remain inaccessible after this quest are the two quest-specific gates outside Bruma: the Bruma Gate and the Great Gate.

If you have killed an NPC and are not yet a member of the Dark Brotherhood, sleeping in any bed in the Shrine will prompt a visit from Lucien Lachance. His speech may be interrupted by members of the Mythic Dawn attacking him. A way to prevent this is to sleep somewhere where no Cultists near enough to detect him or by not sleeping at the Shrine at all.

When power attacking during this quest, sometimes your character will scream out phrases just like an actual member of the Mythic Dawn (e.g. 'Die unbeliever!' and 'For Lord Dagon!')

Bugs
 
This bug can also be caused by attacking any of the acolytes while Mankar is still giving his speech, then quickly returning to the previous room. Specifically, one otherwise smart strategy would be to shoot one of the acolytes with an arrow from atop the ledge, then exit to the previous room, in order to lure that individual so that you can pick them off one-by-one. When you return to the altar, however, you will immediately get the message that Mankar has escaped, even though he is still standing there. This can easily be avoided by waiting until after he has finished his speech and passed through the portal before attacking any of the followers.
 
 
 
 
If you manage to kill everyone in the room before Mankar finishes his speech w/o being detected i.e. console kill everyone independently, once he leaves through the portal, the game will still play the scripted audio introducing you from Harrow, as well as asking you kill the sacrifice despite those characters being dead.
If you save the game while Mankar is giving his speech while standing behind him, he can become invisible when the save is loaded w/o exiting the game i.e. quick loading after being detected.

Journal Entries