The House of Horrors

Background
"I have met Molag Bal, the Lord of Domination, He has asked me to cleanse his altar in the abandoned house in Markarth by luring a priest of Boethiah to him."

Walkthrough
This quest is given when you visit the Hold of Markarth. You will search an abandoned house with Vigilant Tyranus. (if he is not there, refer to this video: Skyrim - House of Horrors (Trouble starting the quest?)) Once you get down into the basement Molag Bal will speak and command you to kill Vigilant Tyranus. Or if you choose not to, Vigilant Tyranus will try to escape but the front door will be locked and Malog Bal will convince him to attack you. Either way you must kill him, so do it and journey down to the altar of Molag Bal in the basement. A scroll of calm will not convince Tyranus not to attack you, and it is unknown if a high enough illusion calm spell will.

Molag Bal entraps you while activating the mace and tells you that he wants revenge on his rival Boethiah and her followers. He wants you to lure Logrolf the Willful, priest of Boethiah to him so he can take his soul.

The location of Logrolf the Willful is random, any Forsworn camp can host him. Travel to his location and free him, be sure all enemies at his location are dealt with as he will immediately run to Markarth. If you've completed the Quest No One Escapes Cidhna Mine, then the Forsworn holding him may not be hostile.

Once back inside the abandoned house, follow Logrolf back to the altar. He will become trapped and Molag Bal will tell you to take up his mace and bash Logrolf to death. Attack Logrolf (you do not need to use the Mace) until he submits his soul to Molag Bal. Once he submits, you are then told to kill him. Do so to receive the Mace of Molag Bal.

Note: This is a good opportunity to level up the one-handed skill and the restoration skill. Equip the mace with one hand and have a Healing Hands spell on the other. Keep hitting Logrolf until his health is close to 0 then start healing him. You can keep doing this for as long as you want, but be sure you do not kill him and that he does not submit before you are done levelling up.



Note: If the shrine holding the mace is activated from the side or from behind you will still be able to move around the room when talking to Molag Bal. (Xbox 360/PS3) On PC, the player is transported inside the trap upon activation of the shrine.

Easter Eggs

 * There is a Poltergeist reference when Tyranus decides to flee the house and get help. The table near the exit of the house has chairs stacked on it in reference to the movie.

Bugs

 * At random times, Tyranus will enter the house and then enter again. The problem with this is now he will continue to stand in the center of the first room instead of going deeper into the house. This will make the quest impossible to complete due to the basement needing a key to open and this effect can only removed by the Daedric Prince telling you to kill Tyranus. A way to force Tyranus to the basement is to hit him. Getting him to attack you then run to the basement, once there kill him and the quest will progress.
 * An extension of the above bug, if you kill Tyranus while he stands in the center, but leave before going to the shrine in the basement, then your vision may be permanently red and hard to see with, and seemingly as impossible to fix as the above bug. This can be fixed by going to Shearpoint, after you've done the Dragon Rising quest, and killing the dragon there. This seems to fix the coloration. I have not tested it yet, but it may also fix the rest of the bug [i.e. not being able to leave after talking to Molag Bal.]
 * Another way to fix your vision is to drink Sleeping Tree Sap. When the sap wears off your vision should return to normal.
 * I have tested both ways (going to Shearpoint and drinking sleeping tree sap) because I had the red vision problem too. The only one that worked was drinking the sleeping tree sap. I think it's the solution to try first.
 * It's not really a bug, but when you return to the abandoned house to hit Logrolf with the mace to death, you can easily keep leveling up by healing him and beating him with the mace. You can also crouch behind Logrolf while beating/healing him and you will increase your sneak too. Just be careful when sneaking because depending on your stats/class you can do a lot of critical damage. This will make you go higher with restoration, one-handed, and sneak skills fairly quickly. This works especially well with lower level players who want to pump up their thief skills. Keep doing it until you're bored.
 * If you pickpocket Tyranus and take everything he has he will not move deeper into the house. If you go into the basement and cause the house to start shaking and then go outside the entire world will also be affected and will shake mercilessly. Upon returning to the house you can kill him and speak to Molag Bal, but the front door will now require a key and you will be permanently trapped inside.
 * After you speak to Molag Bal you may have some trouble exiting the house [you require a key]. If you have a saved game before you spoke to Molag Bal load it up, kill Tyranus and exit the house. My vision hasn't changed at all.
 * If you have killed Grelod the Kind, but have not yet slept, sleeping in the bed will take you out.
 * If you arrive in Markarth via the drinking contest from "A Night to Remember", the innkeeper at Silver Blood Inn might not have the appropriate rumor and will never have the appropriate rumor to start this quest and Tyranus will never be outside the house or outside the city. Even using console commands to force start the quest or spawn a Tyranus does not work in this case. The cause of this bug is that the Forsworn conspiracy quest does not start properly, as it is supposed to start with a murder in the market as you enter the town for the first time through the main gate *** You MAY be able to fix this bug by going to the market, stealthing and killing Weylin while in stealth. If done correctly you will not get a bounty or attacked and the other people will start yelling about the Forsworn attack, thus triggering the quest to proceed corectly. After you should be able to start the House of Horrors quest correctly as well.
 * There is also a bug that Malog Balwill not speak at all and you will have no instruction to further the quest, the best course of action is to just kill Vigilant Tyranus as you will be killing him anyway.
 * Stop the constant shaking by killing Tyranus and exiting the house without going to the altar, though there still may be problems with the visuals such as the gamma levels.
 * While beating Logrolf into submission he may pop out of the trap and stand outside of it. He is still unable to move and the quest is still completable.