To add to this great advice, if you feel lazy to start, get a good audio book and listen as you walk. It becomes a kind of reward for going for a walk, you get a chapter or two of a great book.
An audio book at that time, however, is a great solution. Audio books, for me, can't occupy my entire mind. I can't sit and listen to an audio book. At the same time, they occupy enough of my mind that I can't do other mentally intense things and pay attention to the book at the same time. I had used them for driving, yard work, and other boring tasks to quiet the noise in my head and the feeling of boredom[0] that the task occupies.
When walking with a good audio book, I can observe the world without the noise of my circumstances and it really is a peaceful exercise.
[0] For me, boredom drives depression.
Although the reality is the mind is anything but idle for those predisposed to depression. The rumination, negative thought patterns and self-critical thoughts are worse than a prison sentence of solitary confinement.
For those who may not understand this, imagine standing over a 5 year old constantly berating them, in a horrifically negative way, for every action they take, good or bad. Now imagine the effects of that over years or decades.