Upon completing Riddle of the Vault, you received a note and a crystal. The note is from High Priestess Harla Dar to Cyenadros which states:
"Cyenadros, see to it that this crystal is destroyed after viewing its directive. We cannot have just any earth walker prancing in here and dunking this gem into the spirit pool. - High Priestess Harla Dar of the Awakened"
Inspect the crystal of command. You are told to find a place where the crystal will do something.
Go to the Pool of Spirits( 152, 41, 146 ) /waypoint 152.4, 41.1, 145.5, and ensure that you get an update that you have found the Pool of Spirits before doing the following instructions, else when you hail the Voice of the Palace he will tell you to "Go away". You may have to move to the other side of the pool before getting the update.
Jump into the pool. Examine the Crystal again to get the first update.
The crystal definitely has magical properties, if not some form of creature inside of it. You are told to toss the crystal into some sort of pool of apparitions, ghosts, ancestors, spirits or something!
A certain spot on the Pool of Spirits can be interacted with, using your mouse pointer. Right-click and throw the crystal into the pool.
The quest will tell you to speak to the spirit. You will be on a timer. The Voice of the Palace has spawned at the bottom of the pool. Just hail him to get the next update. You have 90 seconds to hail him after throwing the crystal into the pool.
Visit Tayil outside, in Tenebrous Tangle on the Hidden Refuge.