Excavations at Gran Dolina. This site is world-famous due to the discovery of human fossils dating back approximately 800,000 years. During 1994 and 1995, 80 human fossils belonging to a least six individuals were found, along with 200 stone tools, in level TD6. The find was important because it challenged the idea that humans did not migrate to Europe until 500,000 years ago. Gran Dolina is one of several sites in Sierra de Atapuerca, Spain, that have been studied on and off over the past century, leading to a massive advancement in the understanding of human evolution. In 2000, Sierra de Atapuerca was made a world heritage site by UNESCO.