Brú na Bóinne consists of the three big passage tombs Newgrange, Knowth and Dowth, but there are many other Stone Age monuments in this area in the Boyne valley : mounds, barrows, henges and smaller passage graves. Check out this link. Brú na Bóinne is a UNESCO World Heritage Site. The original complex of Newgrange was built between c. 3200 and 3100 BC. Knowth and Dowth date from about the same time. Read more about them in books or on internet.

Wikipedia-links to Newgrange, Knowth and Dowth

It's been more than 20 years since I visited these megalith monuments, so the photos were not taken with a digital camera. In those days they were still excavating at Knowth. One side of the mound looked fine, while the other side was a mess. Dowth has not been excavated at all recently, but there were much damage to the mound and the passages about 150 years ago. The Royal Irish Academy dynamited the roof causing the still visible crater, though it was pillaged by Vikings and earlier looters long before that.