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
someone
king
I am a king of the whole empire. I give rules and pursuit them. I am brave and fearless.
How do you know the existence of this tunnel? My family has supplied the king with vegetables for many years. In times of war and blockades we have used this tunnel to deliver fresh food to the castle.  I see. What is the plot about? It is dastardly. They plan to steal all the priceless art from the castle.  Why would they do that? I guess they cannot sneak them through here, these tunnels are so small. They plan to pose as restoration artists, painters, construction workers. You must carefully screen everyone that comes into the castle.  Thank you, I will let the royals know about this evil plan. How do you want to be rewarded? I am but a humble farmer and servant of the king. No reward is necessary Where is your farm located? I will make sure your belly is filled with quality meat for years to come. Over the hill and across Old Man Barkley's stream, as the crow flies.  Good! Will you be leaving the same way you came in? These tunnels are a maze, there are about five different rooms in the castle that connect to this very room. I will be returning as I came. I know these tunnels well. 