Even on a tight schedule, Newgrange & Brú na Bóinne earns the hours.
Allow Half to full day.
Standing inside a chamber built before the Pyramids, with its famous winter-solstice light box, is a genuinely awe-inspiring brush with deep prehistory. The honest catch: access is only via timed shuttle from the visitor centre with no guarantee of a same-day place, it's about an hour north of Dublin, and you can't visit the monument independently.