I have three kids. All of them like to climb. Margot seems unnaturally compelled to climb things — no matter how imprudent. (She broke her clavicle at age 2 after climbing up to, and falling off of, the kitchen table.) Unfortunately, our San Francisco postage stamp yard has no good places to climb. Since I spent most of my childhood in a tree, the lack of climbable structures for my kids disturbed me. So, during a recent break between jobs, I built a climbing wall in our house. The kids love it and it was a hit at our recent holiday cookie party.