One of those things is climbing trees. Did you get to do that? I did. It was the best.
In our very small backyard, we have this slightly sick and sad tree that grows in the corner. Our neighbors hate it - they cut off the branches anytime they grow over the fence. The thing is, it has become a great elementary climbing tree for the kids. My older boys used to climb it, now the little kids do. They love it as much as any backyard playstructure. And it didn't cost us a dime!
Simple things - going back to basics