From wow.incgamers.com

Tempest Keep

Summary

• Location: Netherstorm, Outland
• Level: 70
• Layout: 4 wings including one 25-man wing
  • The Mechanar (Level 69-72 mobs)
  • The Botanica (Level 70-72 mobs)
  • The Arcatraz (Level 70-72 mobs)
  • Tempest Keep (25-man raid wing)
    • Bosses: Prince Kael'thas Sunstrider.
• You will only be able to get to the dungeon by the use of a flying mount.
• Main mob type are Blood Elves.

Overview

A high-level instance floating east of Netherstorm, where you will encounter Prince Kael'Thas. Tempest Keep is one big structure with three smaller satellite buildings - wings. One of the original wings is now in Azeroth...

Tempest Keep lore

The mighty Tempest Keep was created by the enigmatic naaru - sentient beings of pure energy and the sworn enemies of the Burning Legion. As a base of operations for the naaru, the structure itself possesses the technology to teleport through alternate dimensions, traveling from one location to another in the blink of an eye.

With Outland serving as the strategic battlefront in the ongoing Burning Crusade, the naaru recently used Tempest Keep to reach the shattered land. However, when the naaru set out from their stronghold, Prince Kael’thas and his blood elves quickly raided the dimensional fortress and assumed control over its satellite structures.

Now, guided by some unknown purpose, Kael’thas manipulates the keep’s otherworldly technologies, using them to harness the chaotic energies of the Netherstorm itself.

Though Kael’thas and his minions maintain a tight hold on the keep, a band of draenei recently hijacked one of its satellite structures, the Exodar, and used it to escape Outland. In seeking out other worlds, the draenei, led by the ancient prophet, Velen, hoped to find allies who would stand with them against the Legion and its nihilistic Crusade.

Key for Arcatraz

Key for Arcatraz is available as quest from A'dal in Shattrath City. Involves bringing top and bottom part of key - one half is possessed by Warp Splinter in Botanica, the other half is possesed by Pathaleon the Calculator in Mechanar. Quest [How to Break into the Arcatraz] is available after you complete Ata'mal crystal quest for Nexus-Prince Haramad.

Tempest Keep Attunement

Questline starts in Shadowmoon Valley at a guy named "Oronok Torn-heart"

First you do some small quests for him, then he sends you out to find his 3 sons.

After you have found them and done all quests you get a quest to kill Cyrukh the Firelord (5 man group)

When you have done that Oronok Torn-heart sends you to Shattrath City and there you can pick up 3 quests and in all 3 it stands like this:

"Four trials you must pass before you are deemed worthy of the Tempest key"

"Trial of the Naaru: Mercy (Heroic)" Completes in Shattred Halls, Heroic

"Trial of the Naaru: Strength (Heroic)" Completes in Steamwault and Shadow Labyrinth, Heroic

"Trial of the Naaru: Tenacity (Heroic)" Save the gnome mage at the end of Arcatraz

After all this is done, you get the Tempest Key