L'autel de Dagon est situé sur l'île de l'Hirondelle Noire. On peut y accéder en bateau à partir des bords du lac. It is served by an acolyte of Dagon and is where sacrifices to the divinité are brought, and so is the location of Geralt's duel with Dagon. After the duel, it is also where the Dame du Lac speaks to Geralt about Destin, knights him and gives him Aerondight.