Look at the wooden chest on the ground and complete the horse puzzle on it. Take the drawer handle.
Look at the painting and you'll see it says 1915 on the bottom right corner.
Go to the grate underneath it and use your screwdriver to remove the four screws.
Enter 1915 into the safe and take the key.
Use the key in the keyhole to the right of the elevator.
Proceed to the next Can You Escape level!