The center of Java is also the center of Javanese culture. Here, the great Hindu civilizations rose to power. Later they were replaced by Islamic sultanates based in the kratons (palaces) of Yogyakarta and Solo. Most of Central Java's sights are within easy day trips of one or the other of these two cities.
Central Java Sights
The reason for Yogyakarta's popularity as a tourist attraction is due to the many ancient temples scattered around the countryside within an easy drive from the city. However, Candi Sukuh is actually closer to Solo. Both cities have kratons (royal palaces) that are worth visiting.
The pyramid-like structure of Borobodur is built on and around a natural hill. Construction was started sometime around the beginning of the 8th century. In plan, it resembles a tantric mandala with six square terraces supporting three circular ones. It's been called a three dimensional rendering of the Buddhist conception of the cosmos. The square terraces are covered with carved relief's that can be read as an "instruction manual" for attaining enlightenment.
Just about 10 miles outside of Yogyakarta is the temple complex of Prambanan. This huge complex of Hindu temples was constructed in the middle of the 9th century. The remains of 244 temples have been identified in the complex. They fell into disuse when the kings of Java moved their capital to the East, and then many were destroyed by earthquakes. It was only reconstructed in the later half of the last century. The central compound contains eight large temples along with eight smaller ones.
Tucked away in the mountains near Solo in central Java is one of the more interesting Hindu temples in all of Southeast Asia. The temple of Candi Sukuh is unique not only in overall design, but also in decoration. This place isn't exactly off the map. It's in all the guidebooks, but is definitely off the tourist trail.