Usually, university libraries are not open to the public, and you need a library card to read, but you can study by yourself without any documents. I just don't know what the rules are during the summer vacation. If you just want to teach yourself, there is no need to go to the library. You can teach yourself directly in the classroom. Many students didn't go home during the summer vacation. You can study by yourself at school and prepare for the postgraduate entrance examination. You can join them and maybe make good friends!