Complete the game. Load your cleared saved game file. Go to Brookwood Camp. Use a skull on top of a grave to display a yellow dot in the world map. There will be no other dots leading to it. Go to that location to find a cave. Pop the bubble in the water. Activate the source well. All the lamps except for one will light up. Use the unlit lamp to reveal a door which opens to the developer's room.
First complete the game. Hold R and select your profile to replace all clockworks with Kingdom Force and see Bluebits instead of Sprites from Clockworks during the intermission sequences. Hold L and select your profile to view the ending sequence.