If you have the chance, try to escape from the city for the day, by taking a a train ticket (the DART, Dublin Area Rapid Transportation).
For less than 10 euros, you can use it without limits for 24 hours. The railway takes you to either Dun Laoighre (south) or north to Malahide, two very pleasant coastal cities where you can fill your lungs with fresh sea air! Malahide also has a beautiful castle worth a visit. The small fishing port of Howth is also a nice destination for the day.