[The Tempest Key] allows players to enter The Eye - the center palace of Tempest Keep - and defeat Kael'thas Sunstrider. This fight is required for several attunement quests. The Tempest Key is not used like an actual key, but rather, like the 
[Drakefire Amulet], it is a passive item that attunes you to the instance.
Obtaining the Tempest Key
The Tempest Key is given after a long quest chain that begins after completing the quest-line (starts with 
[70] The Hand of Gul'Dan) for the [Cipher of Damnation] in Shadowmoon Valley. Upon completing the Cipher quest, you will receive (immediately) a letter in the mail from Khadgar, asking you to travel to Shattrath City to speak to him.
[70] The Tempest Key: Khadgar instructs you to speak to A'dal, who sends you on a series of trials.
- [70] Trial of the Naaru: Mercy: A'dal sends you to the Shattered Halls of Hellfire Citadel to retrieve the [Unused Axe of the Executioner]. You must kill all three of the bosses in the Halls. This MUST be done on Heroic difficulty.
- [70] Trial of the Naaru: Strength: This requires two instance runs, both on Heroic: You must kill Warlord Kalithresh in the Steamvault of Coilfang Reservoir and retrieve [Kalithresh's Trident], then travel to the Shadow Labyrinth in Auchindoun, destroy Murmur, and take [Murmur's Essence].
- [70] Trial of the Naaru: Tenacity: Enter the Arcatraz - a satellite of Tempest Keep - and rescue Millhouse Manastorm. This must be done on Heroic difficulty.
- [70] Trial of the Naaru: Magtheridon: Finally, you must enter Magtheridon's Lair and slay Magtheridon, a 25-man raid boss.
Upon completing all four quests, A'dal will grant you the Tempest Key (along with [Phoenix-fire Band]) and you will be allowed to enter The Eye, Kael'thas' sanctum, for the final confrontation with the "Sun King".
Keys required for quests
The following Heroic entry keys are required, and you must be Revered with a certain faction to obtain them:
[Flamewrought Key] (Honor Hold/Thrallmar): Unlocks Heroic Mode in Hellfire Citadel.- [Reservoir Key] (Cenarion Expedition): Unlocks Heroic Mode in Coilfang Reservoir.
- [Auchenai Key] (Lower City): Unlocks Heroic Mode in Auchindoun.
- [Warpforged Key] (Sha'tar): Unlocks Heroic Mode in Tempest Keep.
- The Shattered Halls, Shadow Labyrinth, and The Arcatraz also have their own entry keys; however, only one person in the group with the key or a lockpicker is required to get past them.
