Look into mouse hole from afar.

You gaze into the mouse hole, in which you see an Improbably Coloured House-Mouse, who is trying to invite you in for mid morning tea. Inside the mouse-house, you notice an picture of her and her mouse-spouse, and an Iron Key.

Examine Box

Upon closer inspection, you find that the box is held shut with an Iron Lock, indicating that there is most likely something of value inside. There is a small mouse hole in the corner of the room.