Caoineadh Cu Chulainn
For me, the Celtic soul of Irish music can be experienced directly in the sound of the uilleann pipes. Bagpipes can also be found in other Celtic music traditions, for example in Scotland or Galicia.
Caoineadh Cu Chulainn, the lament of Cu Chulainn, expresses the grief of this mythical warrior who, in a frenzy of killing, killed his own son.
Here it is masterfully interpreted by Davy Spillane in the show Riverdance.