I seem to be absolutly unable to locate the 3rd tablet -- I read some posts at this board
regarding this item but I can't even find the "Y" shaped room !!?!
Where exactly is this room located ? Also, it appears that maybe I need a 2nd crystal in the
round moving section in order to open up the 4th door - is this correct ?

PLEASE GIVE ME A CLUE. THANK YOU.

You need 3 Glowstones to be able to open all the doors. The y is not really an y but an open rectangle (I_I) with two doors and both NEED TO BE OPEN. That's why you need three glowstones ( one for the door in the rotating room and 2 for the doors I mentionned before.
OHHHHHH it's hard to explain but you will know what I mean. Just look around
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