In one of his moments of wisdom, David Eddings observed that a man who has never walked a mile on his own legs has no clear idea how far a mile is.
to which my immediate reaction was not how he was applying it metaphorically, but to think that a mile was out the front door, around the loop until I reach the arterial road, down it to the next complex, then down that complex's road and back up it again.If I turn right there, and go back to my door, it's another half mile. More typically, I turn left and tack on another two to four miles, depending on which route I take. (Four miles being only recently, and still giving my ankles and knees occasional twinges and mild aches.)
Some pedestrian characters will indeed be surprised at how long a mile is. Post apocalyptic, for instance, and trekking to some hope of safety. Or the king kept in ritual purity at his castle until the war forced him out. (Since for him to be surprised you need both his not being used to such journeys, and for him to take one.) Surprised at the distance, surprised at how much your muscles and joints can ache, surprised at how much of an objection your ankles can put up to going down a steep hill.
Most pedestrians, OTOH, will find it rather short. I had to work up to five miles, but then, that's because I hadn't worked up to it all my life for reasons having nothing to do with exercise. Bilbo Baggins's corrupting influence on his nieces and nephews was in part taking them on long walks, but any old hobbit would probably find my five miles pretty typical, even on shorter legs. And then you have a different problem in conveying it: how it feels like to find it ordinary.