Walking is a great functional exercise. It makes you go out and helps with your cardiovascular system and slows down osteoporosis by providing light impact and making you take a bit of sunlight.
(see my article about vitamin D here).
But you could make the most of it and transform your walk into a full-body workout by stoping along your way when you find a handrail, a balustrade, or a bench (you can us the top of the backrest).
The 3 exercises are:
1) Hinge squat (glutes, quads back muscles and grip)
2) Wide push-up (Shoulders and pectorals)
3) Triceps push-up on toes (calves, abs, triceps)
The safer way to introduce those exercises in your daily routine is to progressively increase the number of times you'll do this sequence. Start by doing it once and see how you feel the next day. Then twice, and third... etc...