Depends where you're going and what you class as "fun". If you like castles, there are lots of them in Ireland, both North and South. For natural wonders, try the Giant's Causeway, the cliffs of Moher and The Burren. For excitement, try the Carrick-a-rede rope bridge. For beautiful countryside, just travel anywhere in Ireland. For unspoiled nature, try the West coast.
For evening entertainment, there are lots of small pubs / inns and you can often hear folk singing in many of them.
Lots of places for days out: Ulster American folk Park, W5, Dublin Zoo, etc.