Advice for Ireland trip?

Lots of good suggestions above but I'll add the Aran islands, Connemara, Croagh Patrick, Dingle, Sneem, Valencia, Merrion Square in Dublin and last but by no means least the neolithic passage grave monuments on the Boyne (Knowth, Dowth and Newgrange).

And weathersealed lenses/bodies (even in 'summer'). Wish I was going back there again...