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
traders
king
I am a king of the whole empire. I give rules and pursuit them. I am brave and fearless.
What on Earth are you doing down here? I have come to offer my services to the King. Down in the secret tunnel? That's a bit absurd, no? I'm a resourceful man. Don't you see I'm in this tunnel? Uh... yes I do see you in this tunnel and I am not quite sure why. Look at this pumpkin. I managed to get this large pumpkin into your tunnels, past your guards and spies. What else do you think I could smuggle in for you? Hmm where did all of this experience come from? Not illegal ways, correct? I am naturally gifted my King. Well... what did you have in mind? I don't see any real applications for you unless you can suggest any? As a King all things are accessible to you, but not all things that you desire will be appropriate for you. I can help bring you those things. Again, that is rather vague. What do you think other than keeping you on retainer? I have information that has eluded your best spies, that's how I knew you had a secret desire for pumpkins.