Dublin is exceptionally "layover-friendly" due to its compact size and the proximity of the airport to the city center. If you have a layover of at least 5 to 6 hours, you can comfortably explore the heart of the city. A taxi or express bus (like the Aircoach) takes only 20 to 30 minutes to reach downtown. With 6 hours, you could visit Trinity College to see the Book of Kells, walk through St. Stephen's Green, and enjoy a pint in Temple Bar. If your layover is 8+ hours, you can add a tour of the Guinness Storehouse or Dublin Castle. A critical tip for 2026: if you are flying to the U.S. from Dublin, you will go through U.S. Preclearance at Dublin Airport, meaning you clear U.S. Customs and Immigration before you board. This is a huge time-saver but requires you to be back at the airport roughly 3 hours before your flight, so plan your "Dublin Deep Dive" accordingly.