The entrance gate, car park and souvenir stalls are worthy of a monument à la the Taj Mahal. Sangiran clearly is proud of its WHS status. I arrived by taxi from Solo train station (18km). The station has 5 trains a day to Yogyakarta, so it's a good day trip from there. The Sangiran site consists of a museum, a huge building with a creative layout. However, there are only two exhibition rooms containing skulls, bones and tools.
Sangiran's story is that of 'Java Man", discovered in the fields here in the 1930s. It is part of the species Homo erectus, one in the chain of predecessors to the modern homo sapiens. At about 700,000 - 1,600,000 years old it is the oldest finding in Asia, but a lot younger than the African examples of early hominids. The site is also known for its animal fossils and neolithic stone tools.
I've seen a number of Early Hominid WHS now, and they all struggle to turn their historical fame into a good visiting experience. Sangiran unfortunately is no exception to this. I guess it's best to tick it off quickly and spend the remaining part of the day in nearby Solo. This is a relaxed Javan town with two Royal Palaces and a couple of nice little restaurants.