When you play the first chamber, you will find a room with a fireplace... as a gamer you know, that this room looks suspicious. Near that room a blue barrel can be found. This barrel has to be rolled into the fireplace. The fireplace will open und you can get inside, when entering the fireplace you have to press X in the inside. Then a new room will appear on the map. There is a door on the floor which can be opend with two keys and will lead you to a secret chamber.