Kraton Ratu Boko (Palace of King Boko) is a partly ruined Hindu palace complex dating from the 9th century. Perched on a hilltop overlooking Prambanan, it is believed to have been the central court of the mighty Mataram dynasty. There's a large gateway and the platform of Candi Pembakaran (the Royal Crematorium), as well as a series of bathing places staggered on different levels leading down to the village. The sunset view over the Prambanan Plain is magnificent.
The surprisingly high entrance fee attracts a lot of comment from travellers and it is debatable whether the site warrants the same admission charge as its more illustrious neighbours. The cost can be partially allayed, however, by buying a Ratu Boko–Prambanan combination ticket. This includes a free shuttle between the two complexes, which are located 3km from each other, or it's possible to take an ojek (motorcycle that takes passengers) or taxi between the two.