Now, new discoveries near the tomb have highlighted the importance of the tomb and surrounding countryside to the prehistoric peoples of the region. [Read more about the Newgrange tomb]
The tomb and the surrounding area, comprising is more than 90 Neolithic and early Bronze-Age monuments, are recognized as the Brú na Bóinne World Heritage site by the United Nations cultural agency UNESCO.
Each year, the rising mid-winter sun casts a beam of light through a "roof box" above the entranceway, deep into the mound of the tomb where human remains were once placed in stone niches.
In 2015, archaeologist Joanna Leigh carried out a geophysical survey of the land south of the entrance to the passage tomb, where the extension was planned.
Plans to extend the visitors' center into the area have now been put on hold.
The rows of pits at the eastern end of the buried structure almost exactly aligned with the entrance to the passage tomb.
The excavations are funded by a grant from the Royal Irish Academy and led by Geraldine Stout, an archaeologist with Ireland's National Monument Service, and her husband Matthew Stout, a professor of geography and history at Dublin City University.
Archaeologists now think the buried structure is a Neolithic cursus, or ceremonial avenue, that was built around the time of the passage tomb or relatively soon afterwards.
Archaeologists now think it was a cursus, or ceremonial walkway, which may have been used during the spring and fall equinoxes for ceremonies associated with the passage tomb.
Local historians Anthony Murphy and Ken Williams spotted the circular structure in crop marks that show up in warm weather.