Prison of Sorrow (Dread Realm)

DQ6 Walkthrough - Prison of Sorrow in the Dread Realm.

Walkthrough

Go downstairs to find the Supreme Sage Isaac captured. Talk to Isaac and you will see inside the sage's mind. Isaac's mind has been tortured by monsters.
Return to Gallows Moor and inform Benjamin of Isaac's current state. The Supreme Sage Benjamin will join your party.
Visit Prison of sorrow with Benjamin. Take Benjamin to Isaac and Benjamin will pray for his brother. After talking with both sages, the boss monsters will appear. Defeat both two of them.
Isaac and Benjamin unleashes the sage's power. Mortamor's Castle will fall to the ground.
Leave Prison of Sorrow and go north to visit Mortamor's Castle.