> dialect changes every 20 miles or so

When I first lived in Italy, this was mind-blowing for me as an American from the west coast. I went on a bike ride with the local team I had joined and they stopped for espresso in a nearby town, and the guy who ran the place was like "oh, you're from Padova" when he heard them speaking. An identifiable change in the dialect over a distance you could easily cover on a bike was a huge "wow!" moment for me.

An Italian told me that he married a girl from the next valley and was asked by an elderly relative, 'why did you marry a foreigner?'.