Seaside town recommendation near Dublin as day trip?

What are you hoping to see in the seaside town? Carlingford might be the closet but it's not a bustling spot. Small marina. Might I suggest taking the hour and 15 minute bus ride from Dublin to Belfast. Have the seafood chowder at Mournes, visit the Titanic Museum and surrounding harbor, wander around St. George's Market, visit the Crumlin Road Gaol (prison), take a black cab tour of The Troubles. Buses have wifi and are very comfy.

Claudia, thank you for the suggestion!

But the buses all say 2.5 to 3 hour rides, one way, and the train is 2 hours, one way, going from city center to city center. It's a little over 100 miles one
way. Can you tell me the bus you mean, that takes only 1 hour 15 minutes?

Thanks!

Howth and Malahide are both close-in (city buses).

Belfast is a hundred miles away. For a bus to make it in an hour and a quarter, it would have to be rocket-propelled and have cops blocking all the intersections not on the freeway.

Apologies. Mistyped. One hour and 45 minutes, not 15. It's the X2 Bus Eireann from Dublin airport to Belfast. If you plan accordingly you could take the earliest departure, 6:45am and be in Belfast by 8:30am. Used it last Fall to return from Belfast to Dublin airport and my flight back to London. Bought the ticket the morning of.

And how long would it take from down around the Spire out to the airport -- thirty minutes at least? Then you'd have to add some slop time to make the connection. You're back up to 2.5 at best.

Merely a suggestion Ed. Unfortunate that all you can do is throw water on it. Let Bluewaterquest decide if it's worth the effort.

We did it via the train, and while it is about 2 hrs 10 mins to get there, it's a nice scenic ride and we enjoyed it, 12-18 euro R/T. Our day in Belfast was quite memorable, as Claudia mentioned we did a Black Taxi tour (wow!), saw City Hall, and yes, that Seafood Chowder at Mourne's is excellent.

Have a great trip.
Edit: Note also that you can ask your Black Taxi driver to pick you up at Belfast Central Station, and off you go, they can then drop you where you want to be afterwards.

My suggestion would be Howth. As Ed says, you can get there by regular city bus.

I'd vote for Howth, you can also take the train (DART) directly there. Much closer to the city and nice walks along the shore or take a boat out to the little island and explore there for a few hours. Plus excellent seafood restaurants on the pier.

Howth perfectly fits the bill! Near enough to Dublin, but still the seaside experience (with the bonus of small enough to be easily walkable).

Thank you also for the tips about Belfast, especially the recommendation for chowder, a natural as part of the seaside exploration!

I will be a solo, and am female. Would you experienced travelers still recommend the Black Taxi tour? (Not sure if it's OK to add a new topic to my original question)?

Absolutely! Belfast is a safe, modern city, and you'll have a local to show you around. There were a couple times on our tour where we got out of the taxi and walked around a couple of blocks. The murals and the stories are a little intimidating, but it's all part of the process and it's reflective of the problems Northern Ireland still wrestles with today.
Here's a shot from our tour, showing one of the so-called peace walls.

I was traveling solo. Never felt unsafe in Belfast or anywhere in Ireland. Even drove from Belfast to the West Coast of Ireland and back. If you can do it, go for it. Belfast is an interesting city.

Yes, go for the taxi tour. I also never had any issues while traveling alone in Ireland. (When Dublin city buses were very crowded after some evening event, a local person showed me how to push and shove my way onto the bus...)

Can I just say how grateful I am for your comments!!! How invaluable this is and how generous you all are!! I did not know what to expect - again thank you so much!