4000BC , Loughcrew, possibly the oldest cemetery in the world, tells of Ireland's neolithic cultures, shrouded in myth and mystery. The tombs are located on three different hills. The largest of the three Cairn T has a vernal and Autumunal Equinox which is when the chamber becomes illuminated with sunlight. There is evidence of many uses during the millenia, but it is generally agreed that they were originally built about 4000 bc as burial chambers.