Sliabh na Caillighe ("mountain of the witches") or Loughcrew is a series of Neolithic mounds located in County Meath overlooking modern Oldcastle. Dating from the fourth millennium BCE the site contains numerous magalithic "passage tombs" similar in design to those found in the Boyne valley. That is, the tombs are roughly circular in shape with a narrow passage leading to a central chamber with three anti-chambers in a "cruciform" pattern. The central room and passageway are constructed in the post and lentil style and the roof is composed of corbelled stone. The main site (designated by archaeologists as 'Cairn T') is also oriented to the autumnal equinox demonstrating, in my opinion, that the site is more than merely (or perhaps even primarily) a cemetery.
Unfortunately, most of the tombs were devastated in the 19th century "excavations" performed by amateur antiquarians/archaeologists. The glacial erratic boulders used to construct the numerous tombs are still intact, but have been left open to the elements and the petraglyphs are slowly being weathered away.
Construction of the tombs at Loughcrew was as significant an undertaking as those found in the Boyne valley. Though much smaller than Newgrange, Knowth or Dowth, the glacial erratics used to from the passageways and central chambers of the tombs had to be collected together and hauled up a significant hill. The construction of such a site indicates a highly organized, and probably stratified, culture.
One of the most interesting features of the cairns of Loughcrew are the numerous petraglyphs found on the glacial erratics used in their construction. There are numerous theories as to the meaning of the glyphs, but as of yet the images have not been deciphered. Most agree that there are astronomical significance to many of the icons, but just as many remain totally enigmatic.