What is the origin of the idiom "a walk in the park" and when to use it?

The idiom "a walk in the park" is believed to have originated in the United States, but its exact origin is not definitively documented. It likely arose from the idea that taking a leisurely walk in a park is a simple and enjoyable activity, and thus, it came to be used metaphorically to describe tasks or activities that are similarly easy and straightforward.