The Hill of Uisneach, about 18 km west of Mullingar, is one of the most important archaeological sites in Ireland and one of the least visited — there are no admission booths, no gift shops, and no visitor centre. The 182-metre summit is dotted with earthworks, enclosures, and burial mounds spanning several millennia, with the great Aill na Míreann at the centre. The site was the location of the annual Bealtaine festival in ancient Ireland, a fire ceremony that marked the beginning of summer, and a modern Bealtaine fire is still lit here each year in early May.
Guided tours run by the landowners are the recommended way to visit, particularly if you want to understand what you're looking at — without a guide, the earthworks can be hard to read. The views from the summit take in an extraordinary sweep of the Irish Midlands, and on clear days several county boundaries are theoretically visible. Book tours in advance through the Uisneach website.