It is not as magnificent as Borobudur, and when we went there it had really sufffered from recent violent earthquakes. It was still really interesting to see the difference between prambanan and borobudur, which are both so close physically speaking and so far away from each other in terms of architecture.
Trick : If you have a student card it is 7€ otherwise it is 13€ !
Destroyed in 2006 by the earthquake that hit Java, the Hindu temple has some disappointing features, and I cannot see how it can be any highlight in anyone's trip.
As described before the price is twice as much for non-students.
There you can see the summit of Gunung Merapi which we ascend a day later.
Prambanan contains about eight temples, which you can explore one by one.
If you stay in Yogya you have to attend both temples.
You can book the temple-tour almost everywere (Prambanan & Borobudur, no entrance fees, just transport).