I seem to be in an endless loop between the library and then through to sewers to the large room "guarded" by a narrow passage with the 2 mermaids (at least there were 2 until i had to kill one so I could re-trace my steps[if one can step while swimming] as they were blocking me.
I'm obviously missing something and would appreciate knowing what to do next.
Thanks!

Do you have the glowstones? You need three of them , then go to the rotating room and open there all the doors. Don't forget to take the glowstones with you because you need two of them in the y-shaped room so you can get the last tablet.
Hope that helps
Good luck
junglegirl

You might have the spell VANISH by this time - you can cast that on creatures that are blocking your path, or on yourself, either way it is a moving experience.

Wyv