Dae

Upon reaching a crossroad in the quest Demon Assault he will say the words.

"The gate to the West leads to the creature that is in possession of the page from the Codex of Infinite Planes. The stairs to the East leads to a cavern where a friend is being held by Demons."

These directions are local coordinates based on when you are facing him. So to your east (global north) when standing in front of Dae is the path to save his friend (optional) and to your west (global south) is where the final boss and page from the Codex of the Infinite Planes are.