I explored the whole map and made Devrons quest. I also won every battle except some harder training.
Does anybody know, how I open the hidden passage? I found a lever, but it does not react to anything.
Perhaps I need to open that strange wall in order to access lower level. Or is it a separate matter I do not find the solution either?

I found a lever, but it cannot be interacted. Maybe there is another one somewhere.
Thanks anyway!

Or maybe update the journal, read (click on) what may be said unread. I really don't remember what was mising.