Third piece: Kill Tirik' Rah in Priestess' Court. ( -171, -3, 165 ) /waypoint -171, -3, 165 (He is a triggered spawn by killing both groups of protectors of Tirik who have a 5 minute respawn time. If he does not show up and only the 2 hounds do, kill the hounds and then kill the protectors again until he spawns with the 2 hounds.)
Read the Tome of the Vessel.
Enter Priestess' Court and stand on the spot in front of where the Rin Priestess of the Fyr'Un spawns, where the floor forms a triangle that indents into the raised square area ( -115, 13, 109 ) /waypoint -114.94, 12.86, 108.72
Inspect the Writ of Akh Na'ba from Part 3.The exact location of this small platform is (-116.99, 33.00, 108.71)... where the square altar on the floor is indented a little with a triangle. You have to stand exactly where those sparklies leave the ground, they will lift you up on an invisible platform.
If you're standing in the right place, you'll be lifted up on an elevator. If not, it says that "you must try another location", so you'll have to reposition and read the writ again. You will know that you are close to the correct spot if you try and camp. It will tell you that "you may not camp on a transporter". This can be frustrating as it is very particular as to the exact spot in which you need to stand. The lift is a small rectangle and you should appear to be standing on thin air just above the ground when on top of it.
If you are having difficulty with this step, try summoning Rin Priestess of the Fyr'Un, stand at the given location (-115, 13, 109), kill the Priestess, THEN examine the Writ of Akh Na'ba - in that order.
Note: Personal experience shows that if you go to ( -108, 13, 109 ) /waypoint -108, 13, 109 first and then inspect the item you will be told that the lift is ascending. Something does get activated in that area. Then go to ( -115, 13, 109 ) /waypoint -115, 13, 109 and inspect the item again for the final effect.
The quest will complete when the elevator lifts you up high enough.