If you a music lover and you want to listen to classical music concerts for free, you are lucky, because you have got a lot of options. The best way to enjoy a free concert is to go along to performances by students at music conservatories and music schools. Usually, you can check the concerts’ agenda in their own website. For instance, at Barcelona you may go the ESMUC, The Escola Superior de Música de Catalunya, that is a higher education public institution. Or you can go the Conservatori Municipal de Música de Barcelona . There is also the Liceu Conservatory Foundation .
In Paris, The École normale de musique de Paris regularly organizes such concerts at the Salle Cortot, and also do the Conservatoire national supérieur de musique et de danse de Paris and the Conservatoire à rayonnement régional de Paris (CRR). Some associations also organize suchs free concerts, for exemple Jeunes Talents. And if you want to get the sheet music for free as well, you can visit the Sheet Music Library (pdf).