2 guides, each rated 1 to 5 with the reason — and two lists per place, where you are comfortable and where to pay attention. Nowhere is called dangerous; the specific thing is what helps.
Very safe. Be aware that Auschwitz-Birkenau requires booking well in advance and is an emotionally heavy full-day trip — plan it deliberately, not as a casual add-on.
Comfortable: Old Town · Kazimierz · Podgórze
Kraków Główny — the main station and the bus station at night
Very safe and easy to walk at any hour. The old town is busy with stag groups on summer weekends, which is loud rather than threatening. The Baltic is cold enough year-round to matter and the beaches at Sopot fly flags for a reason. Taxis from the rank outside the station overcharge; use an app.
Comfortable: Długi Targ and the Main Town · Oliwa · Sopot · Gdynia · the tram network
the Sopot strip at night in summer — Monte Cassino street is where the drinking is, and it is loud more than anything else
the beach at Stogi and Brzeźno after dark — empty, unlit and a long way from anything
the Baltic in June — it is colder than the air by a long way and the shelves drop off suddenly
The ratings are this site's own, from the guides' authors and the corrections readers send in; they are not an index. Read the general advice in travel safety tips.