From the World Heritage inscription:
Excavations here from 1936 to 1941 led to the discovery of the first hominid fossil at this site. Later, 50 fossils of Meganthropus palaeo and Pithecanthropus erectus/Homo erectus were found – half of all the world’s known hominid fossils. Inhabited for the past one and a half million years, Sangiran is one of the key sites for the understanding of human evolution.
As a significant paleontology location, Sangiran is worthy of World Heritage status. As a tourist attraction, it was really a waste of time.
This photo is one of two photos I have from Sangrian and all it is, is the entrance to the site. The only thing to see is a small museum, which mostly is replicas of the actual fossils found at the site. The museum looks like it was left unfinished sometime in the 1980s.
All of that and it also required a rather long and expensive taxi ride from Yogyakarta. I ranked this as my #2 most disappointing World Heritage Site.