Krakow is bloody lovely - touristy but for a reason. Worth knowing that loads of bars/restaurants are underground/cellars so it can sometimes be hard to just stumble on stuff. Make sure you take in Kazimierz.
Gdansk and the coast is definitely worth a visit. You can get the train straight there from Krakow and Gdansk has an international airport so you could always fly into Krakow and home from Gdansk. It’s also close to the lake district which is probably the premier nature destination of the whole country:
Cities-wise, would be unusual not to visit Warsaw (and it’s midway between Krakow and Gdansk if you do do that route). Seems to have an unfair reputation as being a bit boring but I love it. Of the smaller cities, Toruń is very nice and doable as a day trip from Warsaw.
Gdansk is my favourite Polish city - it’s wonderful. Krakow is beautiful but be careful with timings - whilst obviously a good thing it can get overrun with school children on their mandatory visit to Auschwitz (avoid the bigger hotels). I’m off to Wroclaw next month.
When we return to Gdansk we’re going to split the trip with Warsaw - the train was incredibly cheap.
Gdansk is a beautiful city and well worth a visit. Loads of nice bars etc, beautiful buildings, take in some of the Solidarity info. There’s plenty to do and when done, or throw in a trip along the coast to Sopot. The beach front is stunning.
Krakow is great also. Be careful with the apple juice and zubrowka in the cellar bars though. Another beautiful city nice to wander around. Absolutely visit Auschwitz if you can although, as silly as this may sound, it was far more affecting that i expected and floored me that day/evening.
I go to Ostrzyce by the lakes most years and its just stunning. Quiet, cheap and the lakes are wonderful for swimming, walks around beautiful hills and forests. Pretty damn idyllic.
Can usually get around quite well by train i have found, both in terms of ease and cost.
Echo the need to visit Auschwitz-Birkenau, but I’m slightly ashamed to say that it didn’t affect me to the extent that I hoped it would. For me because of the site’s vast, impersonal nature I just couldn’t connect with it. Yad Vashem, on the other hand…never cried so much.
Stayed in Warsaw for a bit a few years ago. Would recomend it for a day if you’re passing through, but not for a holiday. Standard, modern city, albeit with a few interesting targets for visiting. Presumably would have been stunning without WW2/USSR etc