Living on the west of Ireland, and not having a car, I used to think nothing of walking 20 -30 miles to visit friends. Normally on quieter country roads.
I used to, and still do sometimes, listen to the rhythm of my footsteps. They generally go in a crude 4/4 time.
That was always a good starting point, and 20 miles or so later, not only would the time pass quicker, not only would I get a lungful of good mountain air in beautiful surroundings, but I would have had a lot of fun messing around with words, patterns, moods, melody lines, and you can build up quite complex structures.
All from listening to the old clogsB.