The Nighthold
The Nighthold is a quest for level 45. It is step 4 of 4 in The Hunt for Illidan Stormrage storyline, the final step. The quest's turn-in marker is in Dalaran at 28.5, 48.2. It rewards 775 experience.
Description
Illidan's soul rests safely within Light's Heart. Take this vessel and deliver it to Khadgar with the following instructions:
When Gul'dan attempts to tear the sky asunder and bring the dark titan into our world, call forth the power of this vessel and release Illidan's soul into his body.
Go now, <name>. We do not have much time. The dark ritual will begin soon.

