The one in the chamber of fate?
You have to do one of 2 things. 1.) pre ordered Fable 2 when it had just came out, or 2.) Play the game on http://funadvice.com/r/14q1vjiooeu and once you are done with that the chest will become openable and you will get stuff depending on the choices you make in the game on the site i linked you to. You can replay this game as much as you want until you get every item. You must have Xbox Live tho.
no problem! any fable related questions you may have ill be happy to help you out with!
Fable 2? Try 3