The Golden Order Principia is one of those prayer books that you can find throughout the countries in between. This prayer book allows you to learn two additional incantations; Radagon’s Rings of Light and Law of Regression. Radagon’s Rings of Light creates large rings of light that can do a lot of damage, while the law of regression allows you to heal any ailments that affect you. Here’s where to find the Principia of the Golden Order in Elden Ring.
To get this prayer book, you must first get to the capital on the Altus Plateau. This is achieved by obtaining at least two Greater Runes and defeating the Draconic Tree Sentinel boss. You can get Greater Runes from Rykard, Godrick, and Radahn to grant you access to the capital. Once you get to town, you need to make your way to the main street and over to the Dragon Wing. Climb the dragon wing and then the tree roots to access Godfrey’s boss room.
Defeat Godfrey and you can search the boss room. Go outside onto the balcony and climb the tree roots to access the upper level of the boss arena. Go out the door, hang left and jump onto the roof. Go through the broken window to access the other part of the upper level. Follow the balcony to the tree root on the other side. Jump onto the tree root and grab the prayer book from the chair hanging from the ceiling. You don’t have to jump on the chair to get the prayer book, standing on the tree roots will work.
https://www.gamepur.com/guides/where-to-find-the-golden-order-principia-in-elden-ring Where to find the Golden Order Principia in Elden Ring?