Horpina:
You'll need to get the prison key from the Apherus watchmen first, so you can open the prison door. I don't think they'll give it up willingly, so you may have to use your considerable fighting talents to convince them. After you defeat Apherus, bring me the Giant Stem of Apherus... I'm going to mount it and hang it over the door...
"Where do we find these Apherus watchmen?"