Behind the wall is a corridor with a door to the outside by the right hand corner.
The corridor turns at right angles and comes along behind the left hand wall.
Four doors on the ends of the rods are used to control this passageway.
On the other side of the passageway is a cell controlled by a chain that used to pass
through the slot high up in the wall.
The idea was that the if the enemy were allowed to enter they could be controlled and prisoners could be taken.

The posts and balls are a modern addition to disable the doors.

It used to be great fun to operate them years ago.