I had arranged for a driver and was somewhat surprised to also get a guide. She suggested going to a silver jewelry factory not far from Borobudur, and it WAS interesting: lots of filigree work. Then we went on to Prambanan. It is a potentially wonderful site, currently somewhat disheveled as a result of the nearby volcanic eruption. Large areas are covered with architectural fragments set out in ordered rows, waiting for conservation. The major temple, the Temple of Siva, had been off limits to visitors, but when we were thre small gorups could go in, earing hard hats and warned that somthing might fall on them. I did not go in, which means I missed seeing the figural reliefs: the exterior has elaborate but repetive abstract decoration, and a few samll panels of trees adn mythical creatures.
The Temple of Siva is ninth century, and is considered by some to be a response to Borobudur, which itself however is sometimes seen as incoproating some Hindu features. Prambanan also sheds light on the interaction of faiths in medievl Java. There are several Buddhist sites here. One of them is earlierr than the site at Borobudur: it is not well preserved, and is not at present really presented to the public at all. There is much to be done to make this a splendidly instructive collection of religous buildings from various periods.
They suddenly closed the site an hour and a half early, which was just as well because it was very hot and humid, threatening rain: we walked back to the car through a potentially fascinating outdoor market, but we were fearing a storm. In fact, it didn't break until I was in my hotel room: then it poured.