The site covers 780 ha and contains around 40 passage graves, as well as other prehistoric sites and later features. The majority of the monuments are concentrated on the north side of the river. The most well-known sites within Brú na Bóinne are the impressive passage graves of Newgrange, Knowth and Dowth, all famous for their significant collections of megalithic art. Each stands on a ridge within the river bend and two of the tombs, Knowth and Newgrange, appear to contain stones re-used from an earlier monument at the site. There is no in situ evidence for earlier activity at the site, save for the spotfinds of flint tools left by Mesolithic hunters.
However, there is evidence that this site was visited repeatedly during the Bronze Age, Iron Age, and Medieval periods, as evidenced by the multiple Beaker, Roman, and Medieval artefacts that were found during O'Kelly's excavations from 1962 to 1975.
Numerous other enclosure and megalith sites have been identified within the river bend and have been given simple letter designations, such as the M Enclosures. In addition to the three famous tombs, several other ceremonial sites constitute the complex including:
Newgrange is the central mound of the Boyne Valley passage grave cemetery, but many other passage graves exist in the environs, including Knowth and Dowth which are of comparable size to Newgrange. Each of the three main megalith sites have significant archaeoastronomical significance. Newgrange and Dowth have Winter solstice solar alignments, while it is claimed Knowth has an Equinox solar alignment. In addition, the immediate environs of the main sites have been investigated for other possible alignments. The layout and design of the Brú na Bóinne complex across the valley has also been studied for astronomical significance.
As well as being surrounded on its southern, western and eastern sides by the Boyne, one of the Boyne's tributaries, the Mattock, runs along the northern edge, almost completely surrounding Brú na Bóinne with water. All but two of the prehistoric sites are within this river isthmus.