I just watched a walkthrough video for it. Are you sure its not a glitch from one of the two sparkles meant to be in that section? One's on a bookcase you're supposed to explore. The other is on a statue you're supposed to investigate to get Odin to level up to Raiden. The sparkle for one of them may have glitched and sent the pixel out of place above the castle wall or something. That's my best guess without a screen shot. The walkthrough video didn't show any sparkles that weren't immediately accessible