I've been to Ireland a fair few times but wasn't until last summer that I actually "did" Dublin for the first time. Was with my boyfriend who's from Donegal, and we stayed with his sister and her friend who've lived in the city for a few years now but has never actually done anything touristy so we did the most touristy thing you can do and went on the hop-on hop-off tour bus. I think there are a couple of different companies who run them in Dublin, but we took the green one from O'Connell St and it was really good, all the drivers were good craic. We stopped at St James's Gate (Guinness brewery), Kilmainham Gaol, Dublinia etc. There's a few different National Museum stops too. There's Phoenix Park and the zoo as well. I suppose the city centre itself, O'Connell Street there's the GPO, the Spire (which is just a ridiculous giant silver spike, but it's funny to watch people strain there neck to look at it!), and endless tacky gift shops too. Grafton St and the streets around it are best for high street shopping. Albeit expensive, Temple Bar is good for drinks and meeting people, and some of the restaurants in the area are very reasonable. It's not a particularly beautiful city, and there aren't as many attractions and sights as other European capitals but there's a really lively and friendly city nonetheless.