The students built a castle out of recycled materials like plastic bottles, ice cream sticks, toilet rolls, and cardboard for their carnival project. They started by sketching their design and then constructing the castle in steps - making the box smaller, fixing the towers, cutting a door and window, and adding flags made from sticks and cardboard. Finally, they decorated the castle by painting it different colors and adding dragons made of paper. The students learned to work as a group, listen to others, and how to make a float.