The Borobudur Temple complex is the overwhelming reason to come here. Walking the galleries from the base to the summit is the experience; the carved relief panels along the lower terraces are among the finest Buddhist narrative sculptures anywhere, and the view from the upper platforms across the Kedu Plain is extraordinary.
Mendut Temple and Pawon Temple form a sacred alignment with Borobudur and are worth visiting if you have more than a day. The Chicken Church in the forested hills to the west is one of those genuinely odd attractions that defy easy description. The Kedu Plain is beautiful cycling country — flat, green, volcanic — and exploring by bicycle is an excellent way to spend an afternoon.