Grimrock

I have completed all of the four levels accessible from the lab via hub keys, and all of Forest >> Swamp levels.
Also I've found the 3-2-1 secret and killed the baddies in the secret area.
I have the four essences, three of which I've placed in the correct areas.
I am stuck in the laboratory / forest / castle / mines / wargland / swamp loop.
I can go through them all, collecting yet more blue gems etc, I've been through so many times there's pieces of pie everywhere, not that I need it as I have unlimited food in the forest from the 1000s of herders I've slain again and again.
I have been given verbal clues from the sleeping pirate in the town, and the witch in the swamp.
Upon returning once again to the lab I dispatch the dark robed figure again and seem to be back to square one.
The only other possible exit I can find is from the mines to a castle courtyard where I am attacked by a lot of robed figures, I could deal with them but I seem to get frozen to the spot, then eventually die.
I just know I've missed something obvious.
Help would be appreciated!

If you have reached the Palace of Ygramul there is truely nothing reach here. So the only possibility is to go on. And there is a very obvious way for that...

Yes the Palace of Ygramul - dead end literally.
I've scoured every inch of the lab, and all of the levels I currently have access to, I can find no way to go on.. I am stuck.
Could you please give me some sort of clue how to "go on"?
If I knew the area where I can go on from that would be a help.

There is a dome in the center of the area were usually in this mod the teleporters appear. There is also a slot to put a gem in and a gem lies in front...

Ok I am in the lab.
Possible teleporter exits that I can see: Gardens of Longanimity, Archive of Wizardry, Tomb of Artaxes, Plunder Village.
Each of these only have one exit that I can find which is back to the Lab.

Also in the Lab there's the teleporter exit (costing 1 x blue gem) to:
The Dark Forest. Exits: Blue Gem teleport exit to Galamdis Castle.
Galamdis Castle. Blue Gem teleport exit to Swamp Raratanga.
Swamp Raratanga. Blue gem exit to Wargland.
Wargland. Blue Gem exit to La Mina Airom.
La Mina Airom. Hub Key exit to the Laboratory, also a blue gem exit to the Palace of Ygramul (dead end).

I have checked all of these areas and their sub-levels and can find no dome with a slot and blue gem in front, other than the exits specified which lead on to the next area or certain doom etc.

I must have done something wrong or broken the game somehow?
How embarrassing