If you are a guest, using it is free, otherwise you may be asked to pay from 0.25-0.5 E to even 1.25 E to use it. Usually it is 1 or 2 PLN. Entering a restaurant or bar and acting as if you were a customer just to use the toilet is considered rude.
You may also take advantage of public toilets, which are mainly paid as well. We would not recommend the blue free portable toilets with the „Toi Toi” name on them, as they frequently lack toilet paper. What is more, their cleanness, due to their free nature, is lather poor.
Public toilets are labeled in a standard manner (a circle or a triangle, as well as a picture of a man or a woman) and can be found, for example, in the Cloth Hall.