Move slowly, using detect hidden level 4 or above to disarm all of the traps.
Fate shift, and run through.
Then you have to travel through the maze, which is just an area with walls that appear and disappear and don't show up on your overview map. (calling it a maze is a misnomer, you have no true choice in path as one path closes only one way opens up, simply follow the only available pathway.) You have to fight some Niskaru along the way. If you're having trouble fighting them as a rogue because they're agile just like you but there's more of them, one effective strategy is to shield bash and shoot arrows instead of meleeing them to counter-attack. You can also use smoke bomb, run away to setup frost traps, and shoot arrows at them again as they approach.
Finally you have to fight the guardian. Fight him, place the amulet on him (must knock him down) and then remove the gem "Tear of Mitharu" from the amulet to curse the guardian, which makes him immobile.
Note that if you fate shift for this fight you'll only get 1XP. To maximize XP, make sure you fate shift during the Niskaru fights instead.
Note that even if you batter down the Guardian, it will stand up again seconds later. This will end only if you place the amulet on it.
Once you've beaten the guardian, pick up the glass of ambient, and return to Grim Onwig, who will be at the dungeon entrance.
If Detect Hidden skill is high enough you can just disarm the traps in the hallway.
It has been suggested to make sure you grab the chest in the middle of the map on the north side before leaving the room, or a wall will close in front of it. It is not known whether this is a bug, but others have reported that the chest can't be opened after this has occured.
A Stone of Autumn (uncatalogued Lorestone set) is found near the entrance of the Blackened Hall.
On a return trip from the guardian, encountering some of the Niskaru attack the Fateless One but this would cause the "Assault" penalty for defending youreslf.
If Buru's Boots are not used to complete this quest, they will remain as a permanent item in your inventory. In order to get rid of them, return to The Blackened Hall, equip them there, and wait for them to break.