Also known as the Portal Tomb, Poulnabrone Dolmen is one of Ireland's most photographed ancient monuments. Built more than 5000 years ago, the other-worldly dolmen (a large slab perched on stone uprights) stands amid a swath of rocky pavements; the capstone weighs 5 tonnes. The site is 9km south Ballyvaughan and visible from the R480; there's a large free parking area and excellent displays.
Poulnabrone was excavated in 1986, and the remains of at least 22 people were found, as well as pieces of pottery and jewellery. Radiocarbon dating suggests that they were buried between 3800 and 3200 BC. When the dead were originally entombed here, the whole structure was partially covered in a mound of earth, which has since worn away. A highly informative Office of Public Works staff member is often on duty, protecting the monument.