The Stanley Parable: Ultra Deluxe

In order to unlock this, you must complete the game with the ‘Freedom’ ending, as hinted at in the achievement tile, which is the one true ending of the game. Luckily, it is the shortest and least complicated ending to achieve, requiring only 6 to 8 minutes of your time (depending on how quick you are). You get this ending simply by following the narrator’s instructions.

This will be the same ending used for Speed Run (90G). Technically, you can earn both achievements at the same time since you do not have to complete the game in order to prepare for that achievement, so it’s your choice whether to do two separate playthroughs or not. Refer to that achievement for more information.

Walkthrough:
From Stanley’s office, walk through the office and down the corridor. Follow the corridor (there are no diverging paths) until you are standing in a room with two doors. Following the narrator, walk through the door on the left and follow the corridor to the meeting room. Exit the meeting room through the door on the far side, take a right and continue until you happen upon a stairwell. Climb the stairs to the top and exit the stairwell, take a right and you will see an open door on the left. This is the boss’s office.

Enter the office and there is a keypad on the wall behind the desk. Listening to the narrator, he will reveal the combination to be ‘2845’ (if you enter the combination before the narrator finishes telling you what it is, you will have to wait about 15 seconds while listening to calming new-age music). After entering it (first, enter ‘8888’ twice for 8888888888888888 (90G)), the fireplace on the wall beside you will open into a dark area. Walk through it until you see an elevator with a down arrow. Press to interact with it.

When the elevator reaches the bottom, follow the path into the ‘Mind Control Facility’. In each of the three larger circular platforms, interact with a button on the desk to continue. After pressing the third button on the third platform, step on the lift and it will ascend automatically. At the top, exit and walk towards the ‘Facility Power’ door. Go through it and walk a little further to reach a console. On it are two buttons; ‘Off’ and ‘On’. Press the ‘Off’ button and the screen will go black. After about 15 seconds, the narrator will begin talking again and you will see a sliver of light in front of you after another 15 seconds. The narrator will continue to talk as the light grows larger and eventually you will be able to step outside. When you do, the achievement will unlock.

Thanks to Baklava for the video: