The Hall of the Cursed is located inside the Temple of Atal'Hakkar. It is accessed by going upstairs from the center-right or center-left exits in the first room after the instance portal. The hall itself is full of Atal'ai trolls, grell servants, and fierce dire trolls.
In order to kill Jammal'an, one must first kill Gasher, Hukku, Loro, Mijan, Zolo, and Zul'Lor, who stand on the six ledges overlooking the Pit of Sacrifice. These mini-bosses can only be reached by going through the Hall of the Cursed. Once all six are dead, the shield protecting Jammal'an will fade, and he will be reachable. The order of the mini-bosses does not matter, unlike the serpent statues in Hall of Serpents.