If you're in DCU then you'll be close to Clontarf and Killester DART stations. From here you can get to the city centre and plenty of people, old buildings,
bridges and the docklands. Or you can keep going on South to Dun Laoghaire with beautiful harbour and buildings.
Stay on the DART even longer and you reach Dalkey originally a viking settlement, then on to Killiney a pebbled beach in a gorgeous bay.
Still going south you reach Bray (of which I may be a bit biased in my opinion) with it's Victorian promenade, bandstand, cliff walk, pebbled beach,
swan filled harbour and some very pleasant natives
The DART stops in Greystones another quaint little town.
There are some beautiful places to see if you want to leave the city and a 3 day go anywhere ticket on the DART is just €16.10.
If you do make it out this way there are a few of us Appugers living in Wicklow, and you never know we might even be tempted to go for a pint

Síle