My first reaction, when I read the thread title, was "Exactly what is the question here?" Then I read your explanation and it all made sense.

For one day, I'd stay in Belgrade. Paris is - well, it's Paris, but it will be Paris next year too. Even my little home town in Massachusetts has enough to keep someone interested for one day. A full day would have to include poking around the antique steam roller parked outside the public works department and the cave where Chief Metacomet used to rest on his fishing trips, but there's stuff to see. Belgrade will be at least as good, probably better.

(Athena53: We spent a week in Edinburgh and two weeks in the Hebrides last summer, it was great, but went to Paris this year anyhow. If you want less-traveled places, consider Scandinavia. Gotland is beautiful and historic. There are lots of other spots.)