With popular destinations such as Blarney Castle nearby, Cork is a good place to stay for three days to explore. The city of Cork is compact and very walkable, and it even has the second largest natural port in the world. There's no doubt that you'll need a car to explore the county, as public transportation, especially in the countryside, isn't incredible, but while you're in the city, it's best to go on foot. There are tons of cafés, great shops and, of course, a pub on almost every corner.
Cork also has an exciting music scene. Plus, if you're planning to spend a week or two in Ireland, you can easily travel to Cork from almost any other city or town in the country, as it's so well connected.