The tour guides emphasized endlessly that these passage tombs are 500 years older than the pyramids and 1,000 years older than Stonehenge. They were also excessively fond of saying that the art on the stones "was open to all of our interpretations and all of those interpretations were correct." I'm not quite sure what our interpretations were, but whatever they were, they were the right ones.
Despite the repetition, the sites are pretty cool. Knowth has many passage tombs and other mounds:
Newgrange has only one. However, unlike Knowth, we were able to go inside it. Of course, photography wasn't permitted so I don't have a picture. We were also allowed to walk on top of this large mound to see where later civilizations had built small settlements (Newgrange is only about 80 meters in diameter, so when I say small, I mean small!).
The amount of work it took to make these is impressive. The large stones that lined the outside of the mounds (seen in the first picture above) were brought from a location 20 km away. It is thought that they were rafted down the river and then log-rolled uphill over a considerable distance to the monument's location.
Whatever their real purpose, clearly they were important structures.