Riannon's Floor is the fourth floor accessed by Hawke in the Grey Warden prison constructed for Corypheus. It can be accessed only as part of the Legacy DLC and can only be entered from Corypheus's Prison - Tower Base and only if Hawke has sided with Larius instead of Janeka at the end of the Tower Base level.
Background
Hawke continues to battle through Corypheus's prison on this floor. Larius joins Hawke as an ally during this level. It is necessary to make use of the Power Nexuses to control magical barriers throughout the prison. If you side with Janeka you will instead be taken to Corypheus's Prison - Daneken's Floor and you do not access Riannon's Floor at all.
Involvement
Legacy (main)
Power Nexus Puzzle
Finished beam puzzle.
In order to obtain a piece of the Legacy armor, Regalia of Weisshaupt, you have to solve the power nexus puzzle. First you must activate each power nexus. The orange barrier is just at the top of the steps at the beginning of the floor; Larius will prompt you to activate this nexus in order to slow down Janeka and her party. The blue nexus is located in the middle of the east side of the map, the green nexus is in the room at the top of the map under the barrier room, and the red nexus is found in the southern most room (to the right of the doorway blocked by the barrier). (See map.) After you've activated all of them, return to the puzzle room.
Location of nexuses.
The orange beam will have to be set in order to escape from the puzzle room after your encounter with a small party of Corypheus' followers. When you return to the puzzle room after the other nexuses have been activated, set up the red beam first, then the green beam. Doing so will align the other two beams and allow you access to the room containing the appropriate head gear for your character's class. (See below.)
Notable items
Codex entry: Locks within Locks, a note in the central room with the blue nexus
Codex entry: A Change of Course, a note in the southernmost room
Codex entry: Helm of Weisshaupt, a book in the central room with the blue nexus
Cowl of the Silent One for mage Hawke, for the Regalia of Weisshaupt armor.
Warden Scout's Cap for rogue Hawke, for the Regalia of Weisshaupt armor.
Helm of the Fortress for warrior Hawke, for the Regalia of Weisshaupt armor.