Dublin comes alive in the summertime, and it's hard to beat the cultural opportunities Ireland's capital offers.
First off, while drinking isn't technically mandatory in Dublin, it is highly encouraged, and any classic tourist experience includes a trip to the Guinness brewery, the Jameson distillery, or a famous pub like the Temple Bar.
Natural wonders like the Cliffs of Moher offer ample fodder for day excursions, as do the numerous austere castles in the city such as Dublin Castle and Drimnagh Castle. Naturally, the warm weather in June marks the start of peak tourism season, but if outdoor time is important to you, you're best served going in the summer.