Judging from the fact that in Krakow there are many schools of higher education, it is required to have many libraries. Thus you can go there and borrow a book. But what's the catch? Libraries require a student ID or library card. You can get that card if you sign library rules and pay a fee. Usually it is around 5 to 10 zloty (a one-time fee). As far as I know, if you are a student the fee is lower that usual.
I have every reason to believe that you will manage this task. I would also say provincial public library which is located on the Rajska 1 street, have a huge assortment of books in different language, not only in polish. So it's an advantage!
With borrowed book, go to the Vistula and enjoy the weather! :)
In the meantime you can go buy icecream on Starowiślna street. There is very popular confectionery and they have very tasty icecreams. I recommend that place of course. In the evening usually is colder than in the noon therefore you can run along the river with your friends.