Really? Wow, then I guess I can be proud on my tenacity!
It was quite an exhausting experience, I only found the way out by using the old trick (I always walked along the wall to my right and after some time finally found the lair of *youknowwho*).
I found this dungeon by coincidence while I was exploring the river by boat. Is it generally no problem to explore like this or can I mess up something in the game by finding places I'm not supposed to - because they are part of a quest or something like that?