The most prominent

"In Indonesian, ancient temples are referred to as candi; thus locals refer to "Borobudur Temple" as Candi Borobudur. The term candi also loosely describes ancient structures, for example gates and baths. The origins of the name Borobudur however are unclear, although the original names of most ancient Indonesian temples are no longer known. The name Borobudur was first written in Sir Thomas Raffles' book on Javan history. Raffles wrote about a monument called borobudur, but there are no older documents suggesting the same name. The only old Javanese manuscript that hints at the monument as a holy Buddhist sanctuary is Nagarakretagama, written by Mpu Prapanca in 1365."
Taken from http://en.wikipedia.org/wiki/Borobudur


And it is located at Magelang, Central Java.
More Accurately,

"Approximately 40 kilometres (25 mi) northwest of Yogyakarta and 86 kilometres (53 mi) west of Surakarta, Borobudur is located in an elevated area between two twin volcanoes, Sundoro-Sumbing and Merbabu-Merapi, and two rivers, the Progo and the Elo."
Taken from http://en.wikipedia.org/wiki/Borobudur#Location

And what's more awesome, Guinness Book of World Record has declared this temple as the world's largest Buddhist temple.
You can go there by public transportation or by car, it is pretty far from Yogyakarta, but worth to see. You could spent hours just for walking around this huge temple, and after that, you can visit the museum to read and see more about the reconstruction of this biggest Buddhist archaeological site.