Wind-up Key
Wind-up Keys are special items in Blue Prince. They are almost exclusively found near Parlor boxes, and their only use is to open them.
How to obtain
One Wind-up Key will always spawn in in the Parlor, on a desk in the corner of the room.
[Upgrade Spoiler: Parlor] One Parlor upgrade causes it to contain two Wind-up Keys instead of one.
Very rarely, Wind-up Keys can be found in other ways:
[Contraption Spoiler: Jack Hammer] By using the Jack Hammer at dig spots- [Major Constellation: Spiral of Stars] From the random item effect of the Spiral of Stars, before the word "showroom" is added
[Lategame Spoilers] A guaranteed Wind-up Key can be found on a table at the very end of the Crate Tunnel.
Regardless of the source, Wind-up Keys may always be found even if another Wind-up Key has already appeared elsewhere, making it one of the most common special items to obtain multiples copies of.
Usage
While holding one or more Wind-up Keys, Parlor boxes can be interacted with. Doing so removes a Wind-up Key from the inventory and plays an animation of the Wind-up Key being inserted into the box, opening it up. Finding and opening the prize box this way is the goal of the Parlor Game and will reward the player with gems. Wind-up Keys used this way cannot be retrieved.