I started walking part of the way to work (about 3 miles) when I hit 50. I thought that if I didn't keep my body reasonably fit in my 50s I would probably be going physically downhill in my 60s. It was difficult at first and I got shin splints for the first few weeks, but I persevered and the splints went. I got to really enjoy the walking, I was quite a fast walker and felt like I was flying along with my feet hardly touching the ground. I used to walk along back streets, across squares and parks as much as possible to avoid the traffic pollution on the main roads.
I liked the fresh air and being out in natural light, especially when it was sunny. I walked through Regents Park and it was great seeing the changes with the seasons. I looked forward to the first crocuses in Spring, then the blossom then the leaves on the trees.
And the ducklings, goslings and cygnets arriving on the lake after Easter. Then the leaves turning gold, red and brown in Autumn.
It made me feel good as well as keeping me fit. It didn't cost anything apart from needing decent walking shoes. And it didn't take much time. Instead of about allowing 40-50 minutes for the vagaries of travelling on the Underground and buses, it took only 10-15 minutes more to walk part of the journey. In the summer I would sometimes take the same route on my way home.
The only warning I would give you is not to overdo it. At the time the government was advising people to walk 10,000 steps a day (about 4.5-5 miles depending on the length of your stride). I started pushing my daily target up to over 20,000 steps a day and ended up doing more than 25,000 steps a day. During my lunch break I would walk 3 times around the block where I worked, a total of about 2,500 steps.
It ended with me getting plantar fasciitis. A painful condition of the foot which is caused by excessive pounding or weight on the muscle sheath on the base of the foot. It hurts to put any weight on it, and I was hobbling around for months. It was extremely painful for the first 3 months, and when I got home I would just lie on the sofa. It took almost a year to get over it.
Since then I have limited my walking to between 10-15,000 steps a day usually. I still enjoy walking though I can't walk as fast as I used to, and feel that it helps both my physical and mental health.