/ Which cities in Poland are nice to visit
ok, so that's my list ;) :
1. Cracow - of course - nothing new
3. Zakopane - welll, maybe just for the weekend. I wasn't sure to recommend... Generally there's wooden architecture, specific culture, beautiful nature and it's worth to see it but ... but in high season there is f*** crowd! And you must prepare to a lot of people, tacky shops and high prices.
4. Przemysl - I like this city very, very much. Small, unusual, calm with beautiful old town and cheap. IZt's very relaxing city. more over it's very near to polish-ukrainian border so you can even go to Lvov for a day or 2. (circa 80 km)
5. Tricity - Gdans, Sopot, Gdynia
I'd like to add that Masurian lakes (which were mentioned above) are worth to see it. there are a lot of small towns and unique landscapes.