There are a few places that make up the site but I decided to see it by visiting Newgrange - which is the easiest to get to, the most popular and (probably) the most interesting.
I found the easiest way to get there without a car was to jump on one of the coach tours that go out there each day. It also means you are guaranteed a spot in a group tour of the site when you arrive. You need to go in with a guide so if you just turn up, you may have to wait until there's a spot.
The site itself is quite interesting from the outside, although it was 'reconstructed' in a way that experts thought it would have looked. The real highlight, though, is when you go inside. The detail in the rock carvings is incredible and it has been so well preserved after all these millennia. There's a good demonstration of how the sun would look during the solstice - gosh it would be quite an experience to be inside the cavern for that!!