A few years ago I moved for work from a town in northern Italy to another. While only 70km away the two places have very distinct accents. After a couple of years people from my hometown would comment on how I sounded as a guy from the new town (people from the second town would never mistake my origins though, so I guess I had a funny mixed accent).

As a Frenchman in Dublin, Ireland, even I could hear a distinct accent difference between people from the north and the south banks of the river.

Now I wonder if the same could be true of Paris and I'm just blind to it because it's my native language.

Northside and southside Dublin are radically different accents. Less so now, with mass media and increased mobility gradually reducing the extremes, but exemplars of each are almost chalk and cheese - like Queen's English vs Cockney.

Northside drops trailing Ts, replacing them with a gentle glottal stop ("give me my coat" -> "gimme me coa'"), "book" may be pronounced "buke", etc.

Southside, at the sterotypical maximum, pushes trailing Ts towards SH and broadens vowels ("are you all right" -> "ore you awl roish" - it's not quite sh, but in that direction).

(I was born in Dublin, my father and his siblings grew up in North Strand in the shade of Croke Park, but I grew up in Galway, so I observed the accent as an outsider when staying in Dublin.)

I can recognize Italian accents and words that are distinct between towns that are < 20 km apart.

I left my country about 10 years ago to come to US. I talk to my parents and friends every once in a while, so my native language is sharp but that's my only interaction with it (I read, write, speak, think, dream etc in (sometimes broken) English exclusively). But a couple days ago my mom was watching TV and I overheard the conversation (by teenagers) in the show she's watching and it blew my mind how tiny tiny little things were different in their accents. I cannot put it into words exactly what was off about them, probably something to do with stress, but it was a shocking revelation. I asked her about it and she said she can't notice any difference. I asked her to switch to some other shows to see if it was idiosyncratic style of these people, but other shows had similar differences. I guess 10 years is long enough for tiny changes in languages.

I am from south east in France (nearby Marseille), now living in Switzerland, and while my accent was fairly tamed for a provençale, before, I have taken a light French Swiss accent now :'

I moved from iowa to minnesota and made some friends from rural wisconsin, my mother was quite amused when a new accent would come out from time to time.

Each one of those are very distinctive, and even eastern Iowa is more like Wisconsin than the rest of the state. You ask any of those people to say a word like "cow" with a vowel and you get different and notable accents. I recall meeting a woman recently who had been born and raised in Seattle, but her parents came from Wisconsin - I knew, because I could clearly hear their accent in her speech.

Another funny one, the more "locally idiomatic" an expression, the heavier is my accent.

No kidding. The way I managed to identify the accents of my own city was to not live there anymore.

Then you come back and suddenly most people have an accent! It's funny.