But with only four hours you will feel very rushed. It takes about 45 minutes to get from Dublin airport into the city center in a taxi in good traffic. I'd skip this for another time.

A 4-hour layover is technically enough to catch a glimpse of the city, but it is considered very tight and requires perfect timing. Dublin Airport is located about 10km (6 miles) north of the city center, and a taxi or express bus can get you downtown in 25–30 minutes, traffic permitting. With 4 hours, you would spend roughly 1 hour in transit (round trip) and need to be back at the airport at least 90 minutes to 2 hours before your next flight for security and boarding. This leaves you with only 30 to 60 minutes in the city—enough to see Trinity College or walk through Temple Bar, but leaving very little margin for error. If you decide to venture out, it is essential to have your boarding pass ready and use the express bus (Aircoach) or a taxi to maximize your time. For layovers under 4 hours, staying at the airport or visiting nearby Swords is usually the safer recommendation to avoid missing a connection.