The Seer is a powerful mage. You met him the first time in Session 27
In his study on an island in the Sabre River
The Seer is a mysterious and powerful mage. According to him, he is a recluse byu choice, and likes to keep visitors away by keeping powerful beasts in his lair.
He has given you the location to the source of the Sabre River. The Tower of Terror inside Flamesmouth Mountain.