Just like when Burning Crusade launched, and the Level 60 raids were put aside in favor of Outland content, when Wrath of the Lich King was released the endgame content for Level 70 became an afterthought...too much effort for rewards that were quickly made obsolete by Northrend gear. Here's a quick look at all of the content that level capped players were enjoying during the Burning Crusade.
The first raid for a majority of players was Karazahn, a 10-person raid located in a haunted tower previously occupied by the archmage Medivh. In the past, Medivh was possessed by the demonlord Sargeras, who used his considerable magical powers to open the Dark Portal, and allow the orcs to enter Azeroth from Draenor. After his death, he atoned for the opening of the Portal by uniting the Horde and Alliance forces for a desperate, and successful, attempt to fight off the Burning Legion's invasion into Azeroth.
Karazahn has a number of unique fights, including one in an opera house that chooses between three scenarios randomly...
a game of chess that you play against the (sometimes cheating) Spirit of Medivh...and one against an undead dragon.
The final boss is atop the highest spire, and pits you against a Burning Legion bigwig, Prince Malchezaar.I've already covered Magtheridon and Serpentshrine Cavern.
You also get to finally put the screws to Kael'Thas Sunstrider for betraying his fellow Blood Elves and throwing in his lot with Illidan. You find him in The Eye, a portion of Tempest Keep floating off the coast of Netherstorm.
Shortly before you fight Kael'Thas, you face his pet phoenix, Al'ar...
and eventually, the man himself. He has a rare chance to drop the Ashes of Al'ar, a pretty bitchin' mount. For this reason, he is still slaughtered by a number of people on a weekly basis.
Anticipated by many since the launch of the Burning Crusade, the Black Temple instance allows you to take on Illidan in his Shadowmoon Valley fortress.
Players can get a history lesson by heading to the Caverns of Time and participating in the Battle for Mount Hyjal from years ago.
This battle, a result of Medivh's desperate attempt to unite the Horde and Alliance to fight off the Burning Crusade, is a timed event that sees your raid take on waves of enemies, with bosses interspersed within. This was playable in real time strategy form in Warcraft III, but it's a neat way to get a different perspective on a familiar fight. The final boss is the Burning Legion lord Archimonde, who lost the original fight to a tree.
The final patch of the Burning Crusade introduced the Isle of Quel'Danas to players.
This Level 70-only area was phased, which meant that the content changed as players accomplished more quests. This area was the site of Arthas' slaughter of the blood elves, and destruction of the Sunwell, the original source of the blood elves' power.
When you first arrive, you are fighting to take the shore from the Burning legion...then eventually you establish some camps further in...then after awhile, an armory has opened, etc. A nearby five-person dungeon, Magister's Terrace, sets the stage for the final raid of the expansion.
Kael'Thas is still alive, albeit in very bad shape after his defeat at Tempest Keep.
He has essentially sold his soul to the Burning Legion, and is using the reactivated Sunwell to summon the ruler of the Legion, Kil'Jaeden, to Azeroth. After you defeat him, you are free to take on Sunwell Plateau, and close the portal that has opened to Kil'Jaeden.
It's important to note that you don't kill Kil'Jaeden, you merely send him back where he came from.