I´ve found two already - one in the queen´s library and one in the room after that with the cages. After that I have got through the whole city, I think I got through every room but one tablet is still missing.

Can somebody tell me please where exactly the last tablet can be found?

How many green gems have you found? I have only one - that from the mermaid. Are there more?

There are more gems and you will need them.

There is a room roughly the shape of a fat "Y". At the top of each arm on the "Y" there are locked rooms. YOu need to get both doors open (and they have to remain open) and flip the levers that are inside these rooms. When you have accomplished that, a secret room will open up at the bottom of the "V" part of the "Y" (sorry, but I don't know how else to describe this area). When you first explore this area, you might note there there is a water passage at the bottom of the "V" section - the secret room will open up ABOVE this passage way, it opens straight ahead (I confused someone else on this). So don't go swimming down, look straight ahead. There is a chest with the last tablet piece.

Now I know you are going to ask me where the other glowstones are.....
I'll have to go read my notes!

Wyv