While it is worth a trip to Temple Bar for the scene, it is definitely tourist-heavy and pricey. However, it is quite central in the middle of Dublin, and as Dublin is quite a walkable city, Temple Bar is a good starting point for an adventure!
Stephen's Green is in Dublin City Centre, just up the street from Grafton Street. It has loads of shops and ice cream parlors and worth a visit!
Its beauty is truly unmatched, and absolutely worth a visit, if only to see where Tal and Erin became engaged! If you plan on going, please know the weather in December might not be optimal for viewing; however, try to avoid the visitor center. Instead, visit Hags Head and take a short walk up to the Cliffs away from tourists!
If you are interested in venturing around the island, Blarney Castle is stunning! Of course, it is also home to the famous Blarney Stone. Kiss it once and you will have the gift of eloquence for always! Tip: if you are planning on seeing different castles in Ireland, do book your tickets online and in advance. A quick Google search of your preferred castles will get you to the right place to purchase tickets!
Cobh is a quaint sea-side town, and was the last port-of-call of the Titanic. If you are interested in traveling down south, do note that Cork is very near and has a lively scene! (Some would say preferable to Dublin). We stayed at a BNB not too far from Cork and Cobh which we highly recommend, the link is attached here!