Well the video clip isn't anything new, there's heaps on YouTube, but there are people here that have either a bad or slow internet connection or have old tired computers so a written explanation is needed. Like this one here...........
http://skyrimforum.com/threads/dawnstar-invisible-chest.3427/
there are a billion hidden chests but this looks like by FAR the easiest one to get.
In my oppinion that one is like ten times as hard, cause I can't get to the right building and I can't get over the wall, etc.Actually it's not the easiest one, the easiest on can be found here.........
http://skyrimforum.com/threads/how-to-get-out-of-whiterun-and-get-to-a-secret-chest.3760/