One note from the last post (and the main reason I took such pains to put in the River Mattock): when you count the mattock, Brú na Bóinne is more than 75% enclosed by rivers. This must have been significant to the builders.
Newgrange and Dowth were created to line up with the sun of the Winter Solstice. Knowth lines up with the Autmnal Equinox.
We toured Knowth first and it was wonderful. Our guide was really excellent. Unfortunately, we were not able to enter the passages and tombs at Knowth as we later were able to do at Newgrange.
Do you have a feel for how these tombs were created? They were sited based on the position of the sun. Then the kerbstones and orthostats (large, upright stones) were placed with lintels between the orthostats forming the passage. In the case of tombs like Newgrange, the central chamber was created from corbelled stones, overlapped then held in place by the subsequent mound.
Each of the main sites covers about an acre of ground and average 10m in height. The mounds themselves consist of alternating layers of redeposited sod, loose stones, and boulder-clay.
Much is made of the neolithic, megalithic art of the tombs, but I myself, obviously, found that much less interesting than the engineering and siting of the tombs themselves.
The sites were often subsequently utilized or altered, but I'm not that interested in that 'recent' history.
Knowth is so richly decorated 'It is reckoned that one quarter of all Europe's neolithic art is held within.' [source]
One of the most interesting things about Knowth is the 18 smaller mounds situated so close to it.
Here's another website about Knowth.
Nice picture of the eastern passage at Knowth: