Talk to Worsh Sharbyin Khufu Desert Depths to enter the Crypt of the Arch Priestess, then find Milia's Guard.

Show Quest Info

Introduction

You received advice from Worsh Sharby. He knew that to gain access to Wraith Tome, Milia's seal must be broken. However, the clue to breaking the seal was buried with Milia.
If you want to find Milia's clue, you should find the guard in the Crypt of the Arch Priestess.

NPC Dialog

You have the key to the Crypt of the Arch Priestess,
which means something must be done about Wraith
Tome. I am going to tell you all that I know. Milia
didn't tell us the method to release the seal. She
must have kept the method to break the seal in
some way, and it was buried with her in the tomb.
Take the key and find Milia's Guard in the tomb.

Quest Completion

The guard looks like a mere statue, is it an illusion?