Everyone in St Canice's Cathedral joins in. "Green grow the rushes, oh, the sweetest hours that ere I spent were spent among the lassies oh", they sing. The old Gothic-style cathedral in Kilkenny city is packed to capacity. The lights are low, the doors are open and Mairead Ni Mhaonaigh of Altan is up on the altar leading us in song.
"Thank you very much, my dear people," says Altan fiddle-player Ciaran Tourish, getting carried away by the surroundings, warming to the role of officiating cleric. The real dean is also here for the concert. Norman Lynas, Dean of St Canice's Cathedral, standing beside the cathedral's Gothic south door, says the night is "marvellous". George Bell, the cathedral's sexton, is also here. Outside it's almost dark and the party is in full swing. The Kilkenny Arts Festival is off to a roaring start. The night also has a certain edge because the hurling team is coming home victorious. The town is decked in flags of black and amber and the parties to welcome the winners of the AllIreland hurling semi-final against Galway are also getting underway.
Feet are tapping along to Miss Ramsey's Reel. Stan and Rhoda Frumkin from Summit in New Jersey in the US, are sitting in a centre pew listening to Altan. They've come to Kilkenny especially for the music. Over from Cahervillahow in Co Tipperary is engineer John Hayes and his wife, Una. Michael and Rita Holohan from Killenaulle, who have travelled south for the concert, sit happily in a pew at the side.
Kilkenny-based Angela Cahill has come along with her mother Bridie Donohue, who is visiting from Durrow in Co Laois, and her husband John Cahill. Spotted also in the congregation are the deputy lord mayor, Martin Brett and his wife, Rena Brett, a teacher at Scoil Ruain in Killenaule.
"It's mad crazy," says Michael Burke, the festival's production manager, who is anxious to ensure that "everyone is happy at the end of the day". Maureen Kennelly, festival manager, is happy with the level of excitement in the town. The play Malone Dies, from the Gare St Lazare Players, has sold out, and to satisfy demand there is an extra performance tomorrow night - the closing night of the festival. It will be "the final happening", she says. The run of Judas, with Adrian Dunbar in the lead, has been attracting packed houses all week long. The reading by writer Richard Ford, another highpoint of the festival, is expected to draw a huge crowd to the Ormonde Hotel today.
And tomorrow, music lovers will be given an even bigger treat when the World Wind Quintet takes to the stage. The acoustics will, no doubt, be dramatic when their music rises to echo around the walls of the Ballykeeffe Quarry, an open-air amphitheatre in Kilmanagh.