Bloxes

This structure is made of Bloxes, what are bloxes I here you ask? 

"Bloxes are building blocks made of interlocking pieces of corrugated cardboard, folded together. Their unique shape and structure make them exceptionally strong and lightweight—you could build yourself a platform to stand on, and then pick it up and move it wherever you need to."

I am not promoting or endorsing these different products, they are just some examples of ways to do things with cardboard. There are many ways that do not need anything more than a slot cut into it and joined to another box.

Makedo

Makedo is a system which allows you to join all sorts of things together, including cardboard whoopee! I will try to get hold of some to try out for the Carnival of Creativeness.
If you look at Makedo's website gallery of structures, there are loads more ideas to see.

Cardboard

Cardboard has been chosen as it is versatile, plentiful, reusable and recyclable. There are a number of different ways of joining it together, from the old school methods of tape, staples and glue to more recent methods of reusable fixings. I will post about those later. Another simple way is to cut slots in the cardboard and fix it that way, this is free and can be, if designed well, very strong.