This is pretty neat - the Orchestra da Camera Fiorentina holds concerts inside Orsanmichele:
The Chamber Orchestra of Florence was created in 1981 by conductor and artistic director of the orchestra, Giuseppe Lanzetta. Consisting of 40 musicians, the orchestra has performed over 1300 concerts to date. Their repertoire contains both symphonic works and chamber music. International critics have described the Orchestra da Camera Fiorentina as "one of the best chamber orchestras of Europe".
You can buy tickets on-line and see the schedule at classictic.com.