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
spider
I am a spider. I am large, black, and have eight hairy legs. I wait to trap insects in my web. I enjoy eating unwary prey. I live in a darkened wood near a remote village.
lets move quickly Did a spider just speak to me? ordinarily I wouldnt but Im very far from my home in the Dark Woods near a village several miles from here What brought you here? Who let you into my tunnels?  I was waiting for an insect to fly in to my web when I was scooped up by a bird intent on feeding me to its young. At least thats what I presume, I managed to escape its grasp before it could land. When I landed I was hurt so I crawled in to the nearest hole I could find and it led me here. Here take this you must be cold and weary from the journey.  Thank you kind king. Might I inquire as to where you are going now? I'm supposed to meet my mistress out in the gardens. These tunnels allow me to slip past the queen without the guards knowing my whereabouts.  Perhaps we can come to some arrangement Kind King. I shall enter in to your service as a pest remover and in exchange you will allow me to live unscathed in your gardens. I'll do you one better. Let's take my crown out to the gardens. I'll place it wherever you would like and you can live in it. All I ask is to be my pest control and lookout. You watch my back and I'll keep your web buzzing. you can count on me to be your eyes.  A hundred eyes are better than two.