Larioth is the location of one of Raidriar's strongholds. Siris travels to this stronghold to retrieve Galath's Datapod in Act I: The Anomaly. Siris encounters the Soulless Raidriar and defeats him before retrieving the Datapod in the fireplace. Larioth is also where the Dragons Ba'el and Pisci are fought and defeated. When finished, it can be explored via the quest Uriel's Dream.
Raidriar's office is where Siris finishes the quest. There are many works of art in Raidriar's stronghold. Many of these resemble Raidriar. The Artwork near the fireplace shows Raidriar slaying someone, likely Ausar due to the presence of the Vile Blade next to the slain figure.