The Grange Stone Circle, on the shore of Lough Gur about 25 minutes south of Limerick city, is the largest stone circle in Ireland — 113 standing stones, a single entrance aligned to the rising sun at the equinox, and an internal earthen bank that may have served as seating for ceremonies. The circle is roughly 4,000 years old, contemporary with the early phases of Stonehenge but considerably better preserved.
The site is on private farmland with a small honesty-box entrance and a short footpath to the stones. Combine with the larger Lough Gur Heritage Centre on the lake, which covers the wider Bronze Age and early Christian archaeology of the area, and the lake itself, where you can swim in summer.