Here's a book for the adventurous do-it-yourself-er!
These are activities that need a grown-up helper and some serious tools. If you are interested in building stilts or a rope-ladder or even a go-cart -- this is the book for you. Projects are broken down into simple, understandable steps. Safety and adult assistance are emphasized.
Check out 23 Things to Do Before You Are Eleven and a Half by Mike Warren, find a willing grown-up, plan a project then head to the hardware store!