OK, I've been running around in there for a while trying to figure out where it is.
I've looked in the Guide thread on the Zeke quests and the book quests and here's the entry on the Labyrinth instance:
The Labyrinth-Look in a corner near the left tower on the map
No idea which tower is meant by the "left tower".
I can readily admit, I might just be dense here, but I'm ready to give up.
Thanks for any clarification anyone could give.