Go to codes at the options menu then type the code in:

Successfully complete the game, then use the rotating solar system model that now appears where the globe was during the main game. You can play the music from the game. Examine the sun in the model for a full screen view of the solar system. Go to the room that had the trapdoor in the floor in the main game. Examine the table to see all of Leonardo Da Vinci's invention models that were featured in the main game. Use the trapdoor to go down to the lower room to see concept art.

The code for the box in the shed is 13, 21, 34.