Oooo, one thing off the top of my head - even if neither one of you like beer, do the Guinness brewery tour. It's a self guided tour through a variety of exhibits that finishes in a bar on the top floor of the building. It's only like 8 stories, but there aren't many buildings in Dublin taller than that - and it's ceiling to floor glass all around, so you can either enjoy your complimentary pint or order something else from the bar and have your drink and enjoy the best views of Dublin city imaginable.

Oh, and the GPO (general post office) - it's where the rebel leaders holed up during the 1916 Uprising that eventually led to Irish independence. You can still see bullet holes if you look - and my mother-in-law swears that it's lucky to buy lottery tickets there. ;)