With its strong stone walls, built partly along the edge of a 10-metre cliff, this was perhaps Gigha’s most imposing ancient fortification. It is said to have belonged to Chibhich (or Keefie), the son of a Norse king, whose story is entwined with the Irish legend of Diarmuid and Gráinne. Gráinne was daughter to the Irish king. Escaping marriage to the aging warrior, Fionn MacCool, she fled north with her lover, Diarmuid, but on Gigha she fell for Chibhich. Diarmuid fought Chibhich, killing him, and the latter is said to be buried in a grave south of the summit.
From ‘Visit Gigha‘