Defeat all enemies in the immediate area then use the amulet to restore much of the destroyed part of the prison. Continue ahead then turn to the left to find a red chest and a Phoenix Feather.
Prison of the Damned Phoenix Feather
Continue along and open the door to the left. After the scene and breaking free from the fury's illusion, head to the right to find health and magic chests. Behind the rubble is another treasure. (Orkos' Cloak)
Prison of the Damned Treasure
Go to the left and kill the Empusa. Executing will yield magic orbs. Scale the wall and make it to the rooftop. Kill the enemies there and use the amulet to restore much of the destroyed part of the prison ahead.
Once fixed, jump off then grapple the massive chains below. Swing across more green objects until you reach a ledge. Follow the stairs down and head to the right to find a decayed chest along the way. Restore it and collect the red orbs then go down the ladder.