Just head to Yalahar by boat and head north straight into the citys' center. Inside the castle there's a stone stairwell to the north-west which leads down to the Gate of Expertise for level 80.
Go through it and head north where you'll be able to find a teleporter. Go into it and use the strange apparatus in the middle of the room to spawn the first wave of Rift Worms, Rift Broods and Rift Scythes. Azerus is invincible at this point and only deals damage.
Note: There is a table to the right hand side which is a good place to stay to avoid most of the monsters.[]
Keep on defeating all of the Rift Worms, Rift Broods and Rift Scythes until Azerus becomes attackable and kill him. Enter the teleporter which spawns on the square you killed him on and go to to this place here in order to be eligible to enter the reward room:
Once you've stood on that spot head back outside through the teleporter to the south and go back up to the ground level of Yalahar. Stay inside the castle and head to the western side where the reward room awaits!
Note: You can only choose one of the rewards here; by using one of these chests you will also get the Yalaharian Outfit.[]
