I'd recommend flying to Lisbon (Aer Lingus - from Dublin or Cork) or Porto (Ryanair - from Dublin only and during summer months).
Train and bus travel are both cheap and reasonable.
Both cities are very enjoyable spots to spend a couple of days. If you go to Lisbon, you could also spend a night in Sintra.
Lots of nice towns by the coast north and south of Lisbon, that have beaches but also established towns. Vilanova de Milfontes is south of Lisbon and there are loads north of Lisbon that are very good for surfing if you have any interest.
I spend some time in the interior in the mountains as relatives have a house there - and I love it there, but probably inconvenient without a car.