Dublin - how many days to allow

It depends on what you like to do. Hiking in the Wicklows will take a full day, easily. If you like cities, there’s plenty to do for 2 days in Dublin. Dublin Castle is interesting; Christ Church Cathedral; St. Stephens Green; Kilmainham Gaol; Trinity College/Book of Kells; the Archaeology Museum would probably all interest you. Have fun!

For Dublin itself, I feel 2 nights, 1.5 days is sufficient, but that depends on what you like doing. There are some walking trails by the Monastic City, Glendalough and a nice waterfall. It’s a little over a hour drive from Dublin, if I remember correctly.

I would do 3 if you are planning on one of those days being hiking the Wicklow mountains.

I usually start by looking at sights, decide which ones are interesting to me, then let that define how much time I need there.

Personally Dublin isn't one of my favorite cities. I was there in May for way longer than I would have chosen. Generally I'd suggest one full day to look around (but that's only enough time enough for a couple sights).

Sights I liked most were the archaeology museum (public and free admission) and the whiskey museum (kind of expensive but informative and entertaining). I enjoyed a free (tip) walking tour, there are plenty to choose from, and a walking tour of Howth. I thought the student led Trinity College tour was decent, the Book of Kells, however, isn't worthy of a long wait. I enjoyed Dublinia and Christ Church but I'm not sure it would be a top pick for everyone. I didn't enjoy Temple Bar or the leprechaun museum and am not interested in the Guiness storehouse. Newgrange is a really impressive sight. I had previously enjoyed a Bus Eireann day tour of the Boyne Valley that includes Newgrange. I was less impressed with the Mary Gibbons tour but it was better than skipping the area.

I"m not a 20th century history buff so I skipped all of the Irish revolution sights (including Kilmainham Gaol). Very little of Dublin castle dates back to the early construction, that's the only part than interests me. Those would be top choices for some.

We did 3 nights and 2 full days and that was good for us - another half day would have been a plus.

And I'm the opposite of Brad, I very much enjoyed Dublin. He is correct - look at the sights and then decide. The archaeology museum is a wow, Dublinia is a fun, hands-on museum about the real vikings with lots of serious information, Kilmainham Gaol is highly rated, both cathedrals are worth seeing. The Dublin Literary Pub Crawl is a very entertaining, interesting evening walking tour. There are two theatres with London-quality performances at bargain prices, and quite a bit more.