Hamamatsu Museum of Musical Instruments is the city's best indoor sight. The collection ranges from Japanese instruments to gamelan, keyboard instruments, early electronic gear, and instruments from across Asia, Africa, Europe, and the Americas.
The museum matters because it belongs here. Hamamatsu is a manufacturing centre for Yamaha, Kawai, and Roland, so the displays feel tied to the city rather than assembled at random. Allow more time than you think if you care about sound, craft, or design.