Settled on a hillside plateau, overlooking Prambanan temple complex and with a view to Mount Merapi behind Prambanan Temple complex, lie the remains of a once grand palace. The palace (kraton) is named Ratu Boko after a King Boko of local folklore, but the real owner of the palace is more likely to have been a king of a local dynasty.
http://indonesia-tourism.com/blog/ratu-boko-temple-yogyakarta/