Malahide

We did this as a day out when based in Dublin (family of 2 adults and 2 younger kids). Very easy to get to the castle, which is a short walk from the train station in Malahide.

The tour of the castle was very well done. Also a large parkland, garden and fairy trail (good for younger ones) are on site or immediately adjacent. I don't think the castle is as dramatic/large as some others perhaps, but with an interesting history, lovely grounds/gardens and easy accessibility from Dublin center it makes a worthwhile and easy side trip.

Also, we ran out of time and did not get a chance to visit the town of Malahide (the train station is about halfway between what looked like a cute little downtown and the castle other way up the road). I wish we'd had time to explore there, maybe walk about and grab lunch. Something else to consider.

We stayed in Malahide last April. It's a cute little village and I had the best meal I've ever had in Ireland there. I cannot remember the name but it was a pub, that brewed it's own beer, and all the food was delicious. We did not, however, go to the castle.

I just stayed there at the end of my Rick Steves 14 day Ireland tour. The castle is okay but the grounds are gorgeous. I spent several hours there. There is an Avoca store and cafe as well. I stayed at the Grand Malahide hotel
And took a taxi to airport. There is really no shopping there. I also did a coastal walk to the next town Portmarnock. There are quite a few restaurants to choose from in Malahide.