this secret tunnel is like a vein to the castle.  It leads to many other rooms within the castle.  This includes passage to the dungeon, the throne room, the kings chambers, and a secret exit to the outside.  You must be careful because the tunnel is small to maintain its secrecy.  There are 5 different rooms to the castle that can be accessed through this room. This also proves as a good escape route as enemies with large armor will not be able to fit through.
Secret Tunnel, Inside Castle
king
the proprietor
I own an inn, pub, or other lodging. I earn money by running a place of lodging. I provide people a place to sleep and food and drink.
I have just wandered here my king! I apologize!  Ok. You know this is a bad situation for you, correct? How so?! This is not a hallway you should know of. I am just looking for architecture decoration in my lodging businesses.  Not anymore. I must put you in prison. You can never talk to anyone ever again. You are being irrational!  I will explaion myslef further, you see this hallway is a secrete. No one should know of it except for myself. It seems so harmless in here... how could it be secret? This is where i have things transported so no one can see. I want nothing to do with that, your Majesty... You found yourself all mixed up in it though. Tell me who knows you are here?