The Irish pronounce it "crack" and you'll find it over a pint of Guinness in any pub. Fun, laughter, chat and good times, and it's almost guaranteed if there's someone in the bar when you walk in.
2 On the same subject, spend a night in Matt Molloy's pub in lovely Westport. Get lucky, and Matt (of great Irish group the Chieftans) will be there with his flute. The pub itself is crammed, dark and ordinary, but the craic is in every crack.
3 And on an associated subject, "trad" they call it - traditional music, and the pub provides the platform. Fiddle, tin whistle, guitar, accordion, flute and bodhran (small drum). Wonderful, but unless you're in a real tourist area in a bigger city don't expect any action until perhaps 9pm.
4 The Wild Atlantic Way runs 2500km tracking the rugged west coast and - along clifftops and beaches and through lovely towns, pretty little fishing villages and wilderness areas - is a treat that gives you the real Ireland.
5 Galway-what's there not to like about this town? Cobbled streets, brilliant central entertainment area, handy to the Aran Islands and the Connemara National Park. Give it at least two or three nights.
6 Leave the Temple Bar area 'til after dark (yes, it's tourist rip-off territory, but it's lively and fun), and take a couple of afternoon hours to wander the Little Museum of Dublin - one of the unsung gems of the city.
7 The Cliffs of Moher on the southwestern edge of the Burren region in County Clare are a terrific blast - imagine the Grand Canyon on the edge of the Atlantic.
8 The Guinness Storehouse in Dublin might be a little thin for those who choose not to enjoy the free pint at the end of it all, but it pulls more than a million visitors a year and is classy and interesting in a Disneyland kind of way.
9 Belfast's Titanic exhibition should be on everyone's list, drawing close to a million people a year. You don't have to be a marine enthusiast to enjoy it.
10 The Giant's Causeway packs inmore than 300,000 visitors a year, but just down the road is a lesser-known natural phenomena worth a look. The Dark Hedges, which featured in Game of Thrones as the Kings Rd, were planted in the 18th century and now form an eerie tangle of trunks and boughs that photographers salivate over.