In pre-industrial times, what was considered "a day's journey"?

I imagine it depends on culture, climate and other factors. A Sabbath day’s journey has been described at various times as approximately ½ mile, 1 mile or 2 miles (depending on how it was interpreted from Joshua: 3, 4–5). Another source estimates a days journey as 32 to 40 kilometers (20–25 miles). However, I seem to remember in school, when discussing Chaucer’s Canterbury Tales, the instructor said that a day’s journey, at least in pilgrimage, was about 8 miles.

Anyone have any insight into this?