I got my massive thighs and rippled calves from both urban and nature hiking. I used to hike 5 miles in town every day back when I had an evening job. My urban hike included a very steep hill. I managed to lose a lot of weight hiking every day a long time ago.
I'm not 80 years old. I hike and walk and lift heavy weights. Just last Saturday I hiked 16 miles in one day. It is now the Thursday after my hike and I'm still sore. There was 3000 feet of elevation gain so that might explain it. Walking is good exercise and it will take you far (literally and figuratively). You still have to watch your intake, though.
I wouldn't worry too much about your weight fluctuations. You should take measurements instead. They are more accurate. You shouldn't weigh or measure daily though. Weekly is plenty. Look for trends, not daily changes.
Female, 5'3", 50, Max squat: 202.5lbs. Max deadlift: 225 x 3.