To go behind the chat bar, first go to a room where you can you down the side of the chat bar. The only place I know of at the moment is a split level igloo. Go down the side of the chat bar. Once you have done that click the other side of the chat bar. This may be tricky. The split will stop you and you will be behind the chat bar!
You can also go to the coffee shop and do this but you won't stop in the middle.