Starfall is the Dornish castle ancestral to House Dayne that is named in the novels but absent from Game of Thrones.
The castle stands in western Dorne at the mouth of the Torentine, where the river reaches the Summer Sea. It is the principal seat of House Dayne, one of Dorne’s oldest and most storied noble families. The Daynes are associated with the title Sword of the Morning and with the ancestral Valyrian steel sword Dawn.
Starfall is important to the novels’ history even when the main action does not take place there. After the rebellion against the Targaryens, Eddard Stark travels to Starfall to return Dawn after the death of Ser Arthur Dayne. The castle is also tied to Ashara Dayne and to lingering mysteries surrounding Jon Snow’s birth.
The television series uses Dorne, Sunspear, and the Tower of Joy, but never develops Starfall as a location. Sunspear is House Martell’s seat, not House Dayne’s. Highgarden belongs to House Tyrell, and Storm’s End is the ancestral castle of House Baratheon.