You've already received very good advice. If you're in Cork City; An Spailpín Fánach, South Main St. usually has trad 6 nights a week. Some of these sessions have really high class musicians such as Séamus Creagh and Aidan Coffee. The Corner House, Coburg St., has sessions a few nights every week. If you're coming to Ireland in July and August it will be the height of the tourist season and a lot of music is put on especially for the visitors and can be of a very mediocre quality and not very authentic. Killarney Town is a good example; it calls itself the tourist capital of Ireland but is the worst place in the country for Irish music. Also, be aware that traditional music, even though very strong, is very much a minority interest in Ireland, so make sure you enquire as much as possible when travelling around, and say you're looking for real traditional music and not the tourist stuff. The Bord Fáilte tourist information offices are unfortunately not always the best source of information - they may be staffed by people who have no interest in trad and you may be guided only to the "official" tourist spots. Anyway, I hope you have an enjoyable holiday and that the weather will be kind.