High Level Instances
Many high-level end game instances will consist of a raid group, possibly up to 40 people depending on the difficulty.
Instances such as Molten Core, Blackwing Lair, Zul'Gurrub and Onyxia's Lair and Ahn'Quirraj save the participants of a raid to itself, preserving the instance long after the raid has disbanded for the evening. In this manner a group can chip away at the massive instance over the span of a week until it resets itself. Players can only be saved to one instance of a specific dungeon at a time, and you become saved when you are in a raid that defeats a boss in that instance. Given the number of high-level instances available the people that run them typically create a schedule.
Like all instances, the higher, end-game instances have better loot, tougher enemies and bosses and more scripting to make them very interesting. Aside from PvP and the battleground, high-level instances compromise a good deal of the time characters spend at level 60.
Floating above the Plaguelands, the necropolis known as Naxxramas serves as the seat of one of the Lich King's most powerful officers, the dreaded lich Kel'Thuzad. Horrors of the past and new terrors yet to be unleashed are gathering inside the necropolis as the Lich King's servants prepare their assault. Soon the Scourge will march again...
 Blackwing Lair
Blackwing Lair is the hold of Nefarion of the black dragonflight, son of Deathwing. It is located at the top of the Blackrock Mountains, and requires 40 level 60's to complete.
Attunement for Blackwing Lair starts outside the instance for Blackrock Spire, where a crumpled note dropped by a nearby guard will lead you to inspect the glowing orb down the hall. You must then touch the orb that resides behind General Drakkisath in Upper Blackrock Spire to become attuned. From that point you can simply touch the orb located down the hall from the Blackrock Spire instance portal. The original entrance could be found shortly after the Rend Blackhand boss fight in Upper Blackrock Spire, right behind where Nefarian stands during the whole ordeal.
In addition to dropping the set pieces for each class' tier 2 armor sets, Blackwing Lair is home to some of the best rare and epic drops in the game.
 Molten Core
Molten Core an end-game 40-man raid instance located in the depths of the Blackrock Mountains.
The entrance is located towards the back of the Blackrock Depths instance, but a quest received on the way to recover some rock directly in front of the MC instance portal allows you to become "attuned" for Molten Core, allowing you to instead enter the instance through a small window right beside the quest giver at the bottom of the Blackrock Mountain main chamber, or to merely talk to the questgiver. Typically a guild expects all of its members to be 'attuned'.
The highlights of Molten Core include the tier 1 epic sets for all classes, and an emphasis on fire resistance.
 Onyxia's Lair
Onyxia's Lair, located in southwestern Dustwallow Marsh, is home to Onyxia, daughter of the ancient Deathwing of the black dragonflight. Her brother, Nefarian, rules over Blackrock Mountain and Blackwing Lair.
The black dragonflight are shapeshifters, and Onyxia's humanform is Lady Prestor of Stormwind. There, she meddles with the internal affairs of the humans. Further questing reveals that she is involved with why prisoners in the stockades were not killed or why the Defias were involved.
Entering Onyxia's Lair requires a Drakefire Amulet, which requires players to go through an elaborate series of quests. Once inside the job only gets harder.
 The Ruins of Ahn'Qiraj
The Ruins of Ahn'Qiraj is a 20-man raid instance behind the gates of Ahn'Qiraj. For this reason it is usually called "AQ20." Construction of a three piece set begins at Cenarion Hold in Silithus and progresses by gaining faction with them by killing the inhabitants of AQ20 and acquiring regeants in the form of scarabs and multi-class drops. The set is comprised of a ring, a cloak and a 1H weapon.
Of interest to all classes is the inclusion of special books that drop from bosses that teach another rank of certain class abilities.
Ages ago, the Gurubashi Empire was split apart when several high priests sough to summon the bloodgod Hakkar. Their efforts were initially stopped but the kingdom lay in ruins. A tribe known as the Atal'ai took to the Swamp of Sorrows to create a great temple in which to summon Hakkar (The Sunken Temple instance) but met with limited success. The true Hakkar could only be summoned within the Gurubashi Empire in the place known as Zul'Gurub. Many high-priests of different animal aspects went in to stop Hakkar but were, in the end, turned to his side.
The Zandalar Tribe acts as your supporting faction in the quests involved in this 20-man raid instance in northeastern Stranglethorn Vale. The raid instance is saved for 3 days from its start.