I just spent a week in Ireland with my entire family: my parents, three brothers (and one girlfriend), and one sister. There were highs, lows (happens when you have 8 completely different personalities traveling together), and memories that will last a lifetime. And that really is the point.
On Day 1, we went straight from Dublin airport to Glendalough in County Wicklow south of the city. You park at the Visitor's Center for free (we skipped the movie inside) and take a beautiful hike through the "valley of the two lakes." Allow a couple of hours to walk to the Upper Lake, and to explore the monastic settlements that have stood at Glendalough for over a thousand years.
Pick up the Military Road outside of Dublin to reach Glendalough - it is one of the most charming 30-minute drives through picture-perfect Irish farms, lakes, and little towns. You'll be driving on the "wrong" side of the road if you're an American but it's easy to get used to. Brush up on your manual driving skills - the cars are cheaper and smaller than the automatics!