Only a 30 minute train ride from downtown Dublin, you can reach Howth. An easy going town with plenty of seafood restaurants offering views of the harbour and surrounding hills. Many people hike along the skyline of those hills or tour the town with it's market, quaint downtown centre and plenty of restaurants and pubs only steps away from the train station.
I had lunch at East Cafe, located in King Sitric hotel, restaurant and cafe. The food was delicious and I recommend sitting at the bar against the window for a view of the harbour during a rainy day.