Gráinne's request for Diarmuid to keep driving West is a subtle reference to other films based on Irish mythology such as Into the West (1992) and Song of the Sea (2014) where characters also travel West on a quest.
The story closely follows the Irish legend of the Pursuit of Diarmuid and Gráinne which goes back to the 10th century AD. The names of the characters in the film are taken directly from ancient Irish mythology.