It used to be that everyone had to be attuned before they could go into Karazhan. Now it completely optional since a rogue can pick the lock so the [The Master's Key] is no longer manditory. However, someone in the raid group has to have it (unless picked).

Anyway, people may be interested in getting attuned anyway since the chain sends you through some good quests and 5-man runs.

Here are the main steps (taken from wowhead):
  1. Complete the quests Restless Activity and Arcane Disturbances given by Archmage Alturus outside Karazhan.
  2. You must then visit Dalaran and talk to Archmage Cedric who will send you to Khadgar in Shattrath City.
  3. Khadgar will give you a quest to retrieve the [First Key Fragment] from a Arcane Container in Shadow Labyrinth. It is located in the room of the last boss Murmur.
  4. Next you need to retrieve two more key fragments from The Steamvault and The Arcatraz. The Steamvaults fragment is found just before the first boss in the water. The Arcatraz fragment is found in the corner of the blue room after the first boss.
  5. Khadgar will now ask you to visit Medivh in The Black Morass and give him the key. You will need to complete the encounter before Medivh will talk to you.
  6. Return to Khadgar in Shattrath and he will give you [The Master's Key].
The above list is all you need to do (well, for the most part). Here are some notes I had to dig around for:

[Optional] To get into Shadow Labyrinth and get the [First Key Fragment], someone in the group will need the [Shadow Labyrinth Key]. To get that, a visit to Sethekk Halls is required.

[Optional] To get into The Arcatraz and get the [Third Key Fragment], someone in the group will will need the [Key to the Arcatraz]. To get that, the following quest chains are required:
  1. Assisting the Consortium.
  2. Warp-Raider Nesaad, the [Key to the Arcatraz] is actually obtained after completing How to Break Into the Arcatraz.
[Required] In order to enter The Black Morass, each player must have completed Caverns of Time: Escape from Durnholde Keep in Old Hillsbrad Foothills and the corresponding quest series, starting with Old Hillsbrad.

Edited by Zargous at July 7th, 2008 - 4:05 pm