Your senses are met with the dank moisture of a secret tunnel. The stony walls are full of lichen and cave moss. Stalactites and stalagmites pepper the small channel, which bleeds in a pinpoint light from a far off point. The chill air of the King's forest whistles through the tunnel interior.
Secret tunnel, Cave
student
guard
I am a guard at the royal castle.  I am brave and strong.  It is my duty to protect the king.
This is a secret tunnel! You are not supposed to be here! I am an apprentice blacksmith. I am learning how to make swords for the knights. You see, delivering emergency shipment of swords is part of our training. Wouldn't you be happy to see me arrive in the castle carrying a cart full of swords if you were under siege? I would indeed, but this area is still a secret tunnel. Only those authorized can actually go all the way through it.  I am so sorry, I did not mean to cause any trouble. You are not unless you try to pass. There are dangers past this sign you are not prepared for, thus you cannot enter. Feel free to roam around but not through this tunnel. I am lost, as I have said. Can you escort me to the nearest exit? 