Cardboard is a wonderful building material. You can do far more with it than you might expect. Use it to make furniture, sculpture, models, and of course play structures. The common way to assemble projects with cardboard boxes is to slap pieces together with duct tape. But tape is clumsy, expensive, will unpeel outdoors in weather, looks clunky, and won't take paint. A cool alternative are these Kevlar-like rivets specially designed for box cardboard. One shape does both sides. The rivets sport a grippy ratchet that clinches them close, yet enables them to be reused. The large button gives them holding power and allows you to make joints that can swing, too. We've found that you need either two people working, or ape-long arms, to squeeze both sides of the rivet pairs. Also, they are really made for the double wall corrugated cardboard of the kind you find in large appliance boxes; on thin cardboard they aren't as prettily snug, but still will hold fine. A set of 100 (50 pairs) is enough for a small maze.
Mr. McGroovy's Box Rivets
$6 per 50 pairs
Available from Mr. McGroovy's
Mr. McGroovy has free plans and some nice tips on where to locate free large boxes.