The act of climbing a tree; tree-climbing (often as play or a simple outdoor activity).
子供のころ、裏山で毎日木登り（木のぼり）をして遊んだ。
When I was a child I used to play every day by climbing trees on the hill behind the house.
猿が高い枝まで木登りしているのを見た。
I saw a monkey climbing up to a high branch.
木登りは楽しいが、安全には十分注意すること。
Tree-climbing is fun, but be careful and pay attention to safety.