Get to the Hammer of Twilight.
While you were in the mine, I was able to figure out where the Hammer of Twilight is being kept. They created it at the Altar of Twilight to the south.
More important than that, the cultists have made a critical error: Cho'gall is personally overseeing its final construction.
Many SI:7 died to bring us this information.
You will also receive:
- 69,400 experience
- 5 83 50 (if completed at level 90)
- 250 reputation with Stormwind