Prambanon was built in the 9th century before Hinduism and Buddhism gave way to Islam on Java. It looks startlingly like Angkor Wat in Cambodia, which I visited in 1999.
The temple was felled by earthquakes and vandals. Locals took home pieces of rubble and built their houses upon them.
It was restored from the 30s to the 50s, with no real plan. A puzzle where they did not know what the original temple looked like.
Because of severe damage from the 2006 earthquake, visitors are required to wear hard hats to go inside the main monuments. As with other temples, sarongs are required too.
Frans recommended we visit Sewu temple, which was built later but before the Hindus left for Bali. We were the only ones there. It reminds me a little of Montmartre, aside from the beheaded Buddha.
Our handsome guide Tri. "Religion is in the heart." He says he's an observant Muslim who drinks an occasional beer and has a tattoo. He has a great sense of humor and speaks fluent German as well as English, Bahasa Indonesia, and Javanese.
Even better than Borobudur, in case you need another excuse to visit Jogjakarta.