Fun for those willing to explore oddly enough. I couldn't get into the barracks on the second canon but I did force myself into the barracks on the third canon. Not that there was a reason to do so, it was just, it was there so I had to try. I think I got all the cubes on the third cannon, but I couldn't turn it to shoot myself up to the tower :( If the post below is accurate then I just couldn't find the right angle to select to box on.