Towards that end, here is a pair of rooms with a secret door and its opening mechanism described:
Like the armory, this room is full of tiny bits of smashed furniture. It also contains 8 lesser automatons (AC 5, HD 2, hp 9 each, #AT 1, D 1d6+1, MV (40’), Save F 2, ML 10). These automatons have made this room their base of operations. They keep a stockpile of ancient human bones in the corner, to use for bartering with the jury-rigged automatons. Mixed in with the human remains are 500 gp, and the wall sconce from room 9. The automatons have no use for the gold, but couldn’t be bothered separating it out from the valuable skeletons. The wall sconce is tarnished silver, worth 100 gp, and has some colored wires sticking out the end. Careful examination will reveal that a portion of the sconce depresses like a trigger.
9. Officer’s Quarters
This room has a heaps of dry-rotted wood everywhere, with fragments of ancient cloth mixed in. It crumbles to the touch and has no structural value whatsoever, thus the automatons have let it lie. There is a mirror mounted on the east wall, in a silver frame. The glass and frame are unbreakable, and will resist attempts to remove them. A bundle of colored wires are sticking out of a hole in the north wall. If the wall sconce from room 5 is brought here, the colored wires reattached, and the trigger pulled, the mirror will briefly be covered in a shimmering purple light, and then the glass will disappear, allowing entrance through the secret door. From the eastern side of the secret door, the door appears as a rectangle of opaque, dull grey metal. There is a red button that if depressed will cause the secret door to open/close.