In the Republic of Ireland, you will need euros (that is where the castle is). In Northern Ireland (where Niamh is from) you will want pounds sterling. You can get away with using euros in the North but be aware that the exchange rate may not be as good.
First of all, it's important to remember that if someone is insulting you, it means they like you. Here's a short list of our favorite Irish slang: Craic: gossip Banjaxed: broken or drunk Bucketing down: heavy rain Codding: joking Cute hoor: person who works things to their own advantage Culchie: person from a rural area Deadly: brilliant Donkey's years: a very long time Eejit: fool Feck off: you can figure this one out yourself Gammy: weird looking e.g. look at his gammy leg Gas: funny Grand: great Grand: alright Grand: fine Grand: not ok Grand: leave me alone Grand: feck off How's she cuttin?: how are you? Jacks: toilet I'm shattered/knackered: exhausted Not the full shilling: not fully sane There's a wee want in him: he's a wee bit stupid Oul fella/ Oul Doll: Father/ Mother Blotto/ Fecked/ Full as a bingo bus/ Full/ Hammered/ In bits/ Langered/ Locked/ Paralytic/ Plastered/ Scuttered/ Sloshed/ Stoving/ Tanked/ Wasted/ Away with the fairies/ wrecked/ Wrote off: DRUNK