Borobudur
What I liked best about Borobudur was actually the time I spent in the local area. I stayed at this homestay with a family who didn't speak more than a few words of English. I rented a bicycle and just cycled or walked around - outside the small touristy town centre, it's basically a well-populated rural area. Overlooked by mountain ridges, themselves thickly forested, everywhere feels lush and green, with tropical fruit and vegetables all over.
People are friendly, often greeting you as you pass, and there are many opportunities to buy street-food.
Bottles of petrol ('bensin') are on sale everywhere - not at some formal location, just on shelves outside people's houses. So I guess the scooters which make up the bulk of the traffic have no problems refilling.
I visited a tofu manufacturer's house. A covered back yard was the location for everything necessary, from squeezing the soy beans, to boiling them up, to pressing the resulting mixture between boards, to cutting it up into blocks and frying them.
Borobudur temple itself was impressive, in part due to its size - it's a landmark from quite some distance away - but more so due to the thousands of intricate carved panels which narrate Buddhist tales, apparently beginning at the earthly (at the bottom) and working up to the heavenly at the very top of the temple.
Although it's a popular place, it's large enough that you surprisingly don't feel too over-crowded. On the lower levels, you can sit in one of the 'corridors' for ten minutes sometimes, without anyone passing. I'm glad I didn't try to go in at sunrise (a special ticket is supposedly available) as the day I was there started off misty - after an hour or two, it cleared up and we got some views of the mountains and surrounding countryside.