The Master's Key (Guide) (Originally posted by Medel)
This is the guide to the questline to get this key (your attunement to Karazhan)
[Step 1] Arcane Disturbances (47,75)
Alturus sends you on a quest with a [Violet Scrying Crystal] to take readings inside the Master's Cellar just nearby. go down each passage, do your work, and return to him.The pond and the well are found inside The Master's Cellar. There are two entrances to the cellar, both are found right next to eachother at (48, 7. One of them leads to the pond, and the other leads to the well.
[Step 2] Contact from Dalaran (47,75)
NOTE: To begin this quest you also need to complete [Step 1a] Restless Activity (53,79 / 50,79), which can be solved parallel with Arcane Disturbances
[Step 3] Khadgar (15,54) in Shattrath.
[Step 4] Entry Into Karazhan (54,44)
The [First Key Fragment] to be found in the Shadow Labyrinth at Auchindoun.
[Step 5] The Second and Third Fragments Terrace of Light of Shattrath City. (54,44)
The [Second Key Fragment] to be found in The Steamvault at Coilfang Reservoir. (Arcane Container)
The [Third Key Fragment] and last key part to be found in Arcatraz at Tempest Keep. (Arcane Container) The Containers hold a elite MOB in them that you will have to kill to get your Key Frag. Don't worry, it isn't anything big. The SL Key is located to the Left of Murmur. The SV Key Frag is underwater to the left as you are approaching the first Boss. And the Key frag in Arc is found in a corner on the right side of the room with all the giant Voidwalker-type mobs, right after the first boss.
[Step 6] The Master's Touch
Take [Restored Apprentice's Key] from the previous quest to Medivh at The Black Morass in the Opening the Dark Portal wing of the Caverns of Time. Once you have completed the event, he will turn it into [The Master's Key]. The only catch with this is that you have to have completed CoT: Escape From Durnhold Keep before you can go into the Black Morass.
[Step 7] Return to Khadgar
Take the key and show it to Khadgar in Shattrath City.
[Step 8] The Violet Eye
Khadgar directs you to return to Alturus with the key and seek help from the Violet Eye who will then start giving you quests in Karazhan.