Cataclysm Classic features six raids available on 10 and 25 player difficulty, as part of Tier 11, 12, and 13 content. Cataclysm Classic raids are available in both Normal and Heroic difficulties, and can be run with either a 10-player or a 25-player group. While gear drops on Heroic are higher item level than on Normal, there is no gear item level difference between 10- and 25- player modes. Characters must be level 85 in order to participate in Cataclysm Classic raids. Raid lockouts in Cataclysm Classic are boss-specific, meaning players can kill each boss in either 10- or 25-player mode during the same week. What this means is that you can, for example, join a 25-player raid at the start of the week and clear as far as possible, then finish up the raid later in the week as a 10-player group to clear the final bosses. In addition to powerful epic loot, players can acquire distinctive mounts from Cataclysm Classic raids, either through rare boss drops or completing meta-achievements.
Throne of the Four Winds is a small, two boss raid located in the Skywall, south of Uldum. The Skywall is a part of the Elemental Plane of Air, where the air elementals made their home ages ago when they were banished from Azeroth by the Titans. The Throne of the Four Winds is Al'Akir's innermost sanctum, where he advises with the Conclave of Wind, a council of four powerful air elementals, masters of the four winds. Presently Siamat, Lord of the South Wind, cannot be found there as he oversees his sovereign's operations in Uldum.
The Bastion of Twilight is a four boss raid in Normal or five boss raid in Heroic, located atop a twisted pillar in the Southwestern corner of Twilight Highlands. It serves as the main base of operations for the Twilight Hammer, and is the lair of leader of the cult, Cho'gall. Taking out Cho'gall is a necessity for Azeroth, but perhaps there is also something more sinister going on here...
Blackwing Descent is a six boss raid located on the Burning Steppes side of Blackrock Mountain. An extension of Blackwing Lair, Blackwing Descent is ruled by a resurrected Nefarian. After Nefarian's death, Deathwing collected the heads of his children Nefarian and Onyxia from the cities where they were on display as trophies, and resurrected them to rule this place. Here Nefarian and other disciples of Deathwing experiment on dragonkind.
Baradin Hold is a three boss raid located in Tol Barad. Technically a Battleground, battles in Tol Barad take place every two and a half hours. After the battle, the winning faction has access to Baradin Hold until they lose to the opposition. Initially only a single boss is available in this prison, but the other two are added as the expansion progresses.