The key hold access to meilorean helm & armor. Pretty good gear for meele, if u short on money.
How to get the key, its by doing a quest given by ser Dario (obviously at windbluff) to give report to castle that they short on supplies for a week.
In quest description, it states that report either to sir Julien or a giard. But to get the key, u have to report to BOTH, & give all the items needed to dario. Make sure to talk to him twice or thrice after quest completed.
PSN ID : MCR_BonZ "Sure.. You make a mistake, or three.. Don't let it get to you"