Yshari Sanctum is both the name of an uberlevel complex located in Caldeum, as well as its final boss room.
The Sanctum was created at the behest of the Trade Consortium of Caldeum. Seeking to make Kehjistan's new capital a beacon of learning, the mercantile rulers worked to unite the Mage Clans and build the Sanctum. The academy came to be filled with treasure troves of arcana, becoming a place of learning and growth for the various clans lead by the famous Archmage Valthek. In recent times dissent has taken over the academy. Numerous students have left or been expelled from the Sanctum due to dissent with the teaching methods and forbidden magics that are said to be the specialty of Valthek. Now the Trade Consortium have suspect that the old Archmage has gone rogue and seeks to empower what remains of his followers with demonic magic. You must put a stop to this before the whole of Caldeum is overrun with evil.
Each part of the maze is home to a boss and a few sub-bosses. On Destruction difficulty, each boss is guaranteed to drop a piece of the Brotherhood of the Vizjerei set, while the sub-bosses have a 60% chance to drop a piece of the Brotherhood of the Horadrim set. Each boss and sub-boss can only drop their own set piece. Both sets must be worn in order to grant the oskills Holybolt, Arcane Blast and Iron Shield necessary to fight Valthek in the Yshari Sanctum.