And this is Kisimul Castle on the Isle of Barra. Seat of McNeil of Barra. The McNeils were a smallish but feared and lawless clan so in the song they would take their galleys and raid (ie reive) other clans on the Hebrides or western seaboard. They pitted themselves against the Scottish Crown itself and the crown's favoured Clan Campbell when that clan was gaining prominence.

https://www.historicenvironment.scot/visit-a-place/places/kisimul-castle/