We have 2 days. What should we not miss? My wife and I and our 2 teenage daughters are going in April.
We enjoyed the Hop On Hop Off bus and the visit of the Book of Kells.
Kilmainham Gaol was an eye-opener.
Although a bit cheezy, we had fun at the "Food, Folklore & Fairies" dinner, at the Brazen Head Pub.
Kilmainham Gaol is an important experience. Grafton Street is fun to wander down and listen to the musicians who are always there. You might also enjoy one of the National Museums (the archaeology one is my favorite, with the gold hoards and the bog people). The hop-on, hop-off bus is a great introduction to the city. If you get one with a live guide, they are very entertaining, and you can use it to get an overview of the city (go all the way around once - about 90 minutes), then use it as transportation the rest of the 24 hour period. The RS book actually has some good suggestions for Dublin, so you might start there for other ideas.