Mages Asunder

Take the northern mouse hole and click the Font of Strength to gain +1 to that stat.

Examine the bookcase to obtain Codex 075: Hierarchy of the Circle.

Return to the entrance room and exit through the door to the next room.

Defeat the Mages and move to the next room.

Examine the bookcase to obtain Codex 076: History of the Circle.

Defeat the Crazy Mages in the fourth room and open the door at the end of the hall.

Kill the Servants then turn into the burning man, open the door and pass through the inferno.

Continue to defeat your enemies until you reach the final room with a book and some Mage Instructors; the book grants Codex 083: The Cardinal Rules of Magic.

Proceed up the stairs to a new room where the Cursed Dreamer is under attack. He grants you his power to turn into a Golem with massive strength.

Continue up the stairs where more enemies await.

The School of Spirit yields Codex 088: The Four Schools of Magic - Spirit, where as the note yields Codex 078: The Harrowing.

Turn into a Golem and destroy the Massive Door.

Defeat the Priests and make your way to the north-eastern room where a School of Creation adds Codex 085: The Four Schools of Magic - Creation.

The south-western room has an Essence of Willpower which gives +1 to Willpower and a School of Primal which gives Codex 087: The Four Schools of Magic - Primal.

In the south-eastern room Stone Golems defend the Font of Strength yielding +1 to Strength and a School of Entropy granting Codex 086: The Four Schools of Magic: Entropy.

Destroy the southernmost door with the Golem form and defeat the Arcane Horror.

Open the door to find a mini-boss named Slavren, a hunger demon. Defeat it.

Use the Fade Pedestal; choose The Darkspawn Invasion.