Hidden doors?

I’m really new to Inform, and I’m making an adventure in which the player starts in a prison cell. There is a trap door underneath the cell, but it say when I play, “You can see trap door under cell”. This spoils the whole purpose of the room. Is there a way to change this? I tried using “undescribed” but I could not go through the door. Please help soon.

Try making it “scenery”. That prevents it from being described when the player looks around, but allows it to be examined and manipulated.