This leads to an empty room 20 feet high by 50 ' long (should just fit in that space). It was a long time ago, but on a previous delve, you killed a wraith who entered the corridor from here
The few time a gold coin hits the plate, it bounces off. If he keeps trying, he could probably get one to stay eventually (sort of like those games you play at a fair)
After listening at the door, you open it onto a simple 20 x 30 room, 30' high, and the extra 10' in width to the right. There is a door on the east wall at the very top of the room. The room itself is swept clean, except there is a gold dinner plate lying on the floor in the exact centre of the room