Glendalough. It's got unbelievable sites. And it's in County Wicklow about 25 miles or so south of Dublin.
Here is some background: https://glendalough.ie/
Glendalough was a monastic site founded by St. Kevin around 800 AD. Some of the monks who translated Plato, Aristotle and other Classical-era thinkers of Western Civilization were at Glendalough. (If you want to learn more about this, the book How the Irish Saved Civilization by American author Thomas Cahill is a popular text, and Glendalough is mentioned in it.)
Today Glendalough is covered by amazing antiquities. And there are great walking paths, including the Wicklow Way (https://www.wicklowway.com/), a 100-mile-long trail I walked in 1999.
Be careful driving! If you're American, the Irish drive on the other side of the road. I have rented a car twice in Ireland, but it takes some getting used to, especially on the back roads of County Wicklow.