That’s what we do in Toruń, and I know for fact that in some other cities with similar urban plan they do the same.

But certainly not in Warsaw.

1. Anna wrote: ‘So, you say “idę do miasta” if you are out of town and actually heading into town.’

This is true because “do miasta” simply describes a direction, stressing the fact that you are not in town. “Do miasta” expresses a pure fact of going to Warsaw, Krakow, Poznan, etc (you say “Jade do Warszawy” not “Jade na Warszawe” – it is the same rule).

2. Anna wrote: ‘And you say “idę na miasto” if you are actually in town (as in: you live there) and are leaving your house (apartment, hotel room, whatever) to wander around a bit.’

This one implies some activity. You are going “out there” to do something more or less important: shop for fancy clothes, submit documents to a bank, meet with friends, etc. The only thing I wouldn’t necessarily agree with, is that Anna says “as in: you live there”. To me, even if you are from out of town, once you are already in it, you can say “na miasto” because it expresses the fact that you simply have some business to do somewhere within the town’s boundaries.

So, “do miasta” and “na miasto” have two different meanings and maybe it is better to remember them as if they were “two different words”?

About an outsider who is visiting as opposed to a local using “do miasta” – as mentioned above, I think that it doesn’t matter whether you are in town visiting but you live outside of it at the time of using the expression “do miasta”. If you are within the town’s boundaries, I think you should still say “na miasto” (some activities are implied).

Same with “Jestem w miescie” as opposed to “Jestem na miescie”. Both imply that you are in town but “w miescie” would mean that you simply ARE somewhere in Warsaw (for example). “Na miescie” would mean that you are actually DOING something in Warsaw. Note that in this case it doesn’t matter where you come from either – as long as you already are within the boundaries of Warsaw, you can say “na miescie” because you went there to do something, not just BE.

In terms of “a night on the town”… – based on the English meaning, it is going out, having fun. In Polish “Jade na miasto” or “Jestm na miescie” could mean having fun but it could also imply that you are will be running some errands like going to a bank – not necessarily fun stuff. The idea is the same though – you are out there doing something.

Sorry about the long comment and hope it will be a bit helpful…