Very clever & unique concept! Great level design, very fun puzzles to solve. I dig the art style too, I dont know why you choose gothic/dark theme in a game about lock & key, but it works!
One thing that I'd add, maybe change the control scheme depending on the gravity, I think it's better you use up/down when you are on the vertical wall, just to avoid accidental death, its confusing enough that when gravity was on the left, right arrow key become move to the left and vice versa.
Regardless, awesome entry! Marvelous job! :)