Liv and I recently made a cardboard castle and had so much fun. I got the idea from The Artful Parent. They have a fantastic newsletter and always send out ideas that I feel like we can do with basic supplies (even better we could recycle our cardboard boxes and toilet paper rolls for this project). I bought a pack of Kwik Sticks (tempera paint in a stick form-dries almost instantly), but unfortunately when I spray painted the cardboard the kwik sticks wiped off (?) We ended up using them on some of the side pillars, but then grabbing our basic acrylics to paint the rest. The kids have loved playing with it!!