Section of the Trapdoor
The trapdoor is a door. It is scenery. It is locked.
Down from the trapdoor is the Empty Basement.
Up from the trapdoor is the Empty Flat.
The description of the trapdoor is "xxx". [Otherworldly only.]
The other description of the trapdoor is "Set into the floorboards is a large metal ring - it's a trapdoor."
Instead of doing anything with the real trapdoor:
say "Trapdoor? What trapdoor?"
Instead of doing anything with the locked other trapdoor:
say "Trapdoor? What trapdoor?"
After examining the other floorboards for the first time:
now the trapdoor is unlocked.
Instead of searching the other floorboards:
now the trapdoor is unlocked;
say "You have found a trapdoor hidden in the floor."
Before going through the trapdoor:
if the trapdoor is real:
say "What makes you think there is a trapdoor here?" instead;
otherwise:
if the trapdoor is unlocked:
say "Terribly slowly, stiffly, heavily, a hinged square of floor lifts: you go through the trapdoor.";
continue the action;
otherwise:
say "Why would you want to go down here? You haven't paid much attention to the floor yet." instead.