Be aware of the sandbags piling up close to the castle's wall. Use them to climb on the wall. Then follow the ledge until you're close enough to jump on the crumbling tower adjacent to. You can jump inside and then fall in order to find the Stonesword Key.
Out of the window, you will land on the rooftop below , where there is an armored stormhawk. The hawk's attack is as aggressive as the ones before, and it can also shoot fire from its helmet. Picking a target to attack is challenging because of its unpredictable movements The best way to defend yourself is to shield yourself from one of its striking strikes and counter strike in the opening. Defeat the hawk and claim the Dazing Cross-Legged gesture that is on the opposite face of the roofing.
Go to the wall where the stormhawk sat, and you'll see an adjacent tower with a platform you could climb onto. Jump on and walk all through the tower to reach the small wooden pathway that leads you to a platform which houses a Smithing Stone.
Turn back around the tower but instead returning to the top where you faced the stormhawk, you should jump onto the adjacent rooftop with the crumbled pillar on it. You will want to use that pillar to reach the roof above you, and then walk around until there is another accessible rooftop.