Elden Ring PC | Ash of War: Flaming Strike from Impassable Greatbridge site of grace

Despite its name, the "Impassable Greatbridge" isn't impassable. Look up for the flaming rocks being shot at you from the trebuchets and avoid them. Double-jumping Torrent (your horse) can work well to avoid them. This video is a location guide and so I cleared the area first.

Ash of War: Flaming Strike
"Ash of War: Flaming Strike is an Ash of War and Upgrade Material in Elden Ring. Ash of War: Flaming Strike provides Fire and Flame Art affinity and the Flaming Strike Skill. Ashes of War can be equipped on Weapons and Shields to modify the Skill or an equipment, or to apply affinities that modify scaling values."
https://eldenring.wiki.fextralife.com/Ash+of+War:+Flaming+Strike

Redmane Castle
"Redmane Castle is a Location in Elden Ring. The Redmane Castle is found in Caelid. It can be reached by crossing the bridge in-front of the "Impassable Greatbridge" site of grace. Follow the path upwards to the castle gate. Circle behind the castle using the path on the right hand side. After disposing of some enemies, there is a gap that you must jump across, it is recommended to use your mount for this section. There will be a small series of stairs leading to a shortcut, a door that can be opened only from the other side. To access the castle itself, you must climb up the ladder near said shortcut."
https://eldenring.wiki.fextralife.com/Redmane+Castle