The solar is one of the outlying towers of La Valette Castle in The Witcher 2: Assassins of Kings. It is there that Foltest's children, Anaïs and Boussy are found during the castle siege in the Prologue.
To reach the solar, Geralt must help the king across a long stone bridge while being pursued by a dragon. Once there, the king is reunited with his children but their reunion is short lived as the Kingslayer, disguised as a blind monk uses the opportunity to kill the king.