Our flight arrives in Dublin at 6 AM. What are some good activities in Dublin that early in the morning?
Arriving in Dublin at that hour will put you in central Dublin from 8-9 AM. Have breakfast, and then visit St. Patrick's, or any other sites you wish to visit there. Most are open by 9. We arrived at 9:30. It was 2 hours before we got to our hotel.
Breakfast. There's a Starbucks right at O'Connell bridge. Near the O'Connell statue. Stroll along the river Liffey. Or enjoy a walk in St. Stephen's Green after visiting the venerable Gerry's Coffee Shop. Greasy spoon with hearty breakfasts. Blue collar not hip or happening.
Dublin Zoo.
Drop your luggage at the hotel and walk to the zoo (http://www.dublinzoo.ie/).
It will keep you awake until you can get a shower and a nap :-)
We arrived in Dublin around 7:30 a.m., and were into the city center by around 9:00 a.m. (taking a bus from the airport). Our hotel was not only nice enough to let us drop off our bags, but they insisted we have breakfast too (no additional charge). You'll probably get into the city around 8:00 a.m. I would guess, maybe a little earlier.
I would recommend dropping your bags off at your hotel, and getting breakfast somewhere first.
Trinity College will be open for walking around. Kilmainham Gaol (a must see in my opinion) opens at 9:30 (you probably won't want to walk that far - take a bus or a cab). The Archaeology Museum opens at 10:00 a.m. Dublin Castle is right there. Or just stroll around.