This monument is not open to public, but I couldn't resist climbing over the fence and the mound itself. There's quite a nice view from the top. To the east you can see a church ruin, and to the west (about 2 km away) you can see Newgrange (bottom right photo).

There are two passages and chambers that lead into this mound. Dowth South is aligned to the setting sun of the winter solstice; the setting sun illuminates the passage and chamber from about 2pm to 4pm on the days around the winter solstice. The chambers in Maes Howe on Orkney and Tholos de El Romeral in Antequera, Spain are also lit up by the setting sun at the winter solstice. (At Newgrange, on the same day, the first rays of the sun enter the passage and lights up the chamber.) Here's a link to a virtual tour into the mound.