Looking for excellent fiction featuring pre-Christian Celtic society, ideally in Ireland

Like the title says, I'm looking for historical fiction on the Celts, particularly of Ireland, featuring their beliefs and societal mores. I'm interested in the Druids especially, the elite priests and poets of ancient Celtic society.

I'm well aware that real historical research has some massive gaps in knowledge of early Ireland. And so I'm willing to suspend disbelief in historical fiction. Thanks for your suggestions!