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.
Oh can't I? And enough with the itsy bitsy please WHAT?!? HOW?!? Y-Y-YOU can TALK?!? HOW can this BE??? Of course, you could just be having an hallucination  I could be I suppose... Oh no. My brother. He's poisoned me again, hasn't he?!? Well you got better last time, didn''t you? Eventually?  I suppose I did, didn't I? Then again... you could be some enchanted spy. One good way to find out! Hold still... Hey! I appreciate the National Enquirer as much as the next person but I prefer to read it before being splatted by it  Maybe you need a closer look! It is my scepter! And what is a National Enquirer??? You ARE a spy, AREN'T you??? Spill your guts or I'll squash them! I dodge you and now I am on the ceiling! That's right you dodge! Because I am the king! And only one of us is going to make it out of here alive. And it's not you!!! hahahahah! Ther are five different ways out of here. I can sneak under the doors  Only if you escape me. I will never stop, and I will never quit until you are found and destroyed.