From the World Heritage inscription:
This famous Buddhist temple, dating from the 8th and 9th centuries, is located in central Java. It was built in three tiers: a pyramidal base with five concentric square terraces, the trunk of a cone with three circular platforms and, at the top, a monumental stupa. The walls and balustrades are decorated with fine low reliefs, covering a total surface area of 2,500 m2. Around the circular platforms are 72 openwork stupas, each containing a statue of the Buddha. The monument was restored with UNESCO’s help in the 1970s.
Borobudur is one of the top cultural attractions in South East Asia. The temple is the largest single Buddhist temple in the world. Lost to most of the world for several hundred years, it was buried by volcanic ash and jungle until the early 20th Century. In the last several decades, the Indonesian government has made restoration of Borobudur a top cultural priority.
Borobudur is an easy drive from Yogjakarta and it can easily be visited in a morning or afternoon, or visited in conjunction with nearby Prambanan.
During my visit to Borobudur I had the pleasure of meeting an Indonesian English class which was visiting to practice their English with tourists. Everyone was interested in Barak Obama, who had spent a few years in Indonesia.
If you visit Bali, a side trip to Yogjakarta is well worth the time.