Toying With The Dead

Background
Once you're a member of the Thieves Guild, you can ask Vekel the Man, the bartender at the Ragged Flagon in Riften, if he has any work he needs doing. He'll reveal that he has a client with particular tastes in literature that can only be sated with the writings of a madman.

Objectives
Find all four volumes of Arondil's journals scattered throughout the ice caves of Yngvild.

Walkthrough
Yngvild

Wander a pretty straightforward path through the ice cave tunnels, dispatching leveled draugr and Yngvild Ghosts as you discover, read, and take each volume of Arondil's journals, Eventually, you encounter a door leading to the next area.

Yngvild Throne Room

Awaiting you in a large cavernous area just inside are Arondil, his Yngvild Ghost bodyguard, and the final volume of his journal. Kill the bodyguard and Arondil, loot his body for his key and whatever other loot you care to take, grab the last volume of the journal and the Stone of Barenziah sitting right next to it on the table. Don't forget the Grand Staff of Calming leaning up against the nearby unlocked chest.

After you pillage, head off down a tunnel to the east, where you'll find a gate that can be opened by activating a lever on the wall to the right (about ten feet from the gate itself). on the other side of the gate are the bodies of a Nord, a Breton, and a Redgaurd holding nothing of note to steal. Open the iron door with Arondil's Key and head up the spiral staircase to a door back to Yngvild.

There you'll find an apprentice-level locked chest, and a secret door through the stone that you open with a lever right next to it; the door opens up on the area near where you found the second journal volume.

Return to Vekel for your reward.