In Assassin's Creed Valhalla Siege of Paris you can get abilities that grant you additional skills. This way, you won't have to rely only on the attacks you unlocked in the skill tree. On this page, you will learn the locations of Books of Knowledge in Melunois.
You can find the Golden Flame ability in Diodurum Ruins.
To get to the skill, you must enter the cave. It is located underwater. Jump into a small pond that will allow you to head further. The underwater path is very straightforward and there are no turns or blockades.
Once you are standing on stable ground, you will see bars behind which is a passage covered in debris. You can open it right away. However, you can also do it later if you prefer. Jump in the water and continue swimming forward.
Your have to destroy the cluttered wall. You can do this with the flammable jugs or with the special skill called the Incendiary Powder Trap.
Behind the wall you will find the treasure. This is a great offensive ability. You can plant bombs near your opponents and run away before you are spotted.