The Radya Pustaka Museum in the Sriwedari park area holds a collection of Javanese royal artefacts including kris, wayang puppets, gamelan instruments, traditional weapons, and manuscripts written in Javanese script. The building is a fine example of colonial-era Dutch architecture adapted for a Javanese purpose.
The museum is small but well-stocked, and it is rarely crowded. The gamelan instruments are particularly fine — you can see the careful metalwork on the bronze keys and understand why a good gamelan set is worth a small fortune. The museum staff can sometimes arrange a brief demonstration on request.