Go to the maquette and move the mini crystals (red and blue) to the balcony of the mini house. Hold the mini aqua crystal over the balcony area. In the house, pull the lever at the side door. Pick up the key, allow it to fall down the stairs, and use the red crystal to push it out the door. Push the other crystals out of the house. Use the maquette to move crystals and key out of the area.