For this Trophy you will have to complete 3 sidequests in the tower. They are:
- Malcolm's Will
- Altar of Dumat
- Paragon's HeirMalcolm's Will:
At the beginning of the tower's first level you'll get this quest. To complete it you'll have to free and defeat three spirits/demons. They are trapped behind magical fields. To free them you have to find and deactivate red orbs called "Mark of the Binder". The demons are along the path you have to take anyway to progress the story so it would be pretty hard to miss them. When you come close to a field you'll hear a male voice. Check the immediate surroundings to find the orbs and deactivate them. They will be close (mostly right next to the field or in the next room).Altar of Dumat:
This quest will be available as soon as you find one of the four ceremonial items of Dumat on either the second towerlevel (Farele's Floor) or the Tower Base.
The four items can be found here:
If you have all four items you can go to the altar and place them on the plates to perform the ritual and complete the quest.
You also have the option to defile the altar which you must do before
you pick up the fourth item. If you decide to do that prepare for a fight against two rage demons and six shades.
Performing the ritual will give you more XP, some coin and a necklace but...you don't like the evil gods...do you? The Paragon's Heir:
On the tower's third level you can find journal entries on the corpses of Legionnaires of the Dead. The quest will be aquired as soon as you have picked up two of them. After you have picked up all three you will get a quest marker that leads you to the body you have to find and perform the rites on.
Here the locations of the journals and the body:
Image credit to Dragon Age Wikia