I got this quest while investigating Ragnvald for a WORD WALL... and soon realizing that I wasn't getting anywhere without doing this quest first. Damn! You too can get this quest by heading to Ragnvald, which is in ruins slightly to the northeast of Markarth. Anyway, HOW you get this quest is by inspecting a tomb of sorts INSIDE of Ragnvald, which I'll detail a little further on.
Once you reach the outskirts of Ragnvald you'll have to take out a couple of Draugr. Head on in and make your way lower into the area. As you can probably guess, the main enemy here is Draugr, and you've likely had tons of experience with them so far. Head lower until you come to an area with two levels. To the right of this area you'll find a door leading to the "Ragnvald Canal" and to the left you'll find a door leading to the "Ragnvald Crypts".
To GET this quest, find the tomb in the middle of this area and check out the skull-shaped indents in it. THAT will give you the quest, and we need to find some skulls to put in the tomb.
Let's head to the "Ragnvald Canal" first. Fight your way through this beautiful area until you see a pedestal with a skull on it. When you grab this skull "Torsten's Skull Key", Torsten will pop out of the grave further on to object. Thankfully he's weak as all get out, but two more Draugr come out to help him. Slay them all and follow the path past the right Draugr to go higher so you can collect some chests and use an iron door to go back to the hub area.
Onto "Ragnvald Crypts" now. This area is pretty linear, so travel onwards killing Draugr until you see a chest in a wall recess. The chest is trapped, so untrap it and loot it, then pick up the RESTORATION SKILLBOOK on the dresser nearby (named "Mystery of Talara, v2"). You'll find another skull as you further explore this area ("Saerek's Skull Key") so take it and get ready for a fight that's almost identical to the Torsten fight you had earlier.
Once you have both skulls, return to the hub area. SAVE before putting them in, as we're about to face another DRAGON PRIEST. Put the skulls in when you are ready to release OTAR the MAD. Get in as many hits as you can as he appears since he is so up close and personal. Heck, you can even stun-lock him pretty easily. He has a POWERFUL lightning attack that can kill you in 2-3 hits if you aren't careful, but you can also use this rooms layout to find places to heal.
Once he's dead, be SURE to grab his MASK (named Otar) and head past the once blocked barrier to claim a chest and the WORD WALL which teaches you the word KYNE - KYNE'S PEACE. Very nice. We are done with this area and this quest.