Creiston Mines - how do I proceed?

[jfun23]

Okay, I killed the evil baron here, and reported back to the king. Went back to the castle, which has now been taken over by some regent. He says that to progress, I have to find the dirigible built by the dwarves for this purpose. I can't find anything of the sort, and it's driving me crazy. Clearly, I'm simply walking right by whatever it is I need, but for the life of me I can't figure it out. What am I doing wrong?