On Citadelle des Morts, you can earn another free perk by completing parts of the main Easter egg. Finish all the steps until you’ve collected all the Summons. You can find the corresponding guide HERE!

Once you’ve completed the necessary steps of the main quest, return to the wall with the symbols and the book. Equip each incantation one at a time and use it on the wall. You’ll notice that each row of symbols begins to glow again. Repeat this process with all the incantations until the wall looks like it did before.

Afterward, you will be locked in the room and must survive three rounds. Once you’ve made it through these rounds, you’ll be rewarded with another free perk.