Totally stackable, invented WAY before the wheel and the very cornerstone of our company, the humble box is one of our absolutely most favouritest things here at SO.
These boxes however have a little trick up their sleeve. They go from flat to glorious box in the blink of an eye, which means your fort building and spaceship travel will be up and running in no time - oh and something boring to do with papers and filing that we're not really interested in.
After some extensive research from the many samples we received (the junior's fort was the tallest / most well defended), we managed to accurately recreate the unfold sequence much to Fellowes' satisfaction. Which is pretty impressive considering all the samples were now totally broken and covered in 'Keep Out' and 'No Girls' drawings by the time we actually got down to business.