To Blind the Enemy Quest

Go to Ab'Dendriel. Go up one floor in the depot and head west. Talk to the NPC Eroth about a mission. He will say you have to destroy an orb in the top of the tower of Elvenbane with a Mirror.

Enter the Elvenbane Fortress here

(you'll need a Destroy Field Rune) and go into the central tower. Go up to the last floor (be prepared to face many monsters, listed above) and use the Mirror on the Scrying Ball you see there.

Report back to Eroth to get your reward.