You decide to inquire about the mystical symbol directly. With respect, you ask the mage in the portrait about its significance and any knowledge that could aid your quest.
The mage gazes at you thoughtfully, and after a moment, they begins to speak. "The symbol you seek is ancient, a key to a hidden realm within the abandon wing of the castle. It marks the entrance to a realm. The mystical symbol will guide you, but caution, for the journey is perilous."
Armed with this knowledge, you feel a sense of purpose as the enchanted symbols on the walls seem to resonate with the wisdom imparted by the portrait mage.