The Witness Cheats
At the start of the game you will see a gate. You can actually connect the sun to it and open it. You can then enter a hotel. Upon getting to end, you will unlock a secret ending.
Once unlocking the challenge (found within the mountain) you can unlock a shortcut which leads you back to theatre room below the windmill. While moving through this shortcut you should come across a drawing of a puzzle solution. Usually these solutions would unlock an extra film sequence in the theatre room. However, this solution is used on the force field which is used as a barrier between the tutorial are and the rest of the island. Use this solution on the panel which deactivated the force field at the beginning of the game and it will create a new puzzle using the sun as its starting point. Upon tracing the pathway, the force field will instead be replace by an entrance to an otherwise inaccessible developer lounge which overlooks the entire island. There you can find a series of audio tapes and a live action sequence which follows a developer (presumably Jonathan Blow) meandering around his office.