during the little publicized Baroque Festival:
Friday, May 25, Templo de Belen (almost across from the Mercado Hidalgo), 9:45am, free. I went to a similar concert there this morning. Although many people came and went, I was probably the only person who came for the music, so I felt as if the marvelous music was just for me.
Wednesday, May 30, 8pm, in The Compania church beside the main University building. 10 pesos admission.