Newsletter.

At the main menu, select "Join the Newsletter" by tapping the down arrow twice and selecting by pressing the "C" key. This will minimise the game and open the Dev's website on your desktop browser and unlock this achievement. There is no need to subscribe to the newsletter to obtain the achievement, you only need to select the option at the in-game menu.

Beware, for me the game locked up when it minimised and I had to force close it in task manager and restart the game. For further information see video walkthrough part 1 from the start, to the 0m35s mark.

Collapse.

This is a story related achievement and is unmissable. This achievement will unlock at the end of the night club scene, for more information see video walkthrough part 1 from the 0m36s mark through to the end of video walkthrough part 2.

Arrival.

This is a story related achievement and is unmissable. This achievement will unlock when the train arrives at the planet, for more information see video walkthrough part 3 from the start, through to the 2m03s mark in video walkthrough part 4.

Ending.

This is a story related achievement and is unmissable. This achievement will unlock when you exit the dream world at the end of the game, for more information see video walkthrough part 4 from the 2m03s mark through to the end of video walkthrough part 6.

No Flying?.

At the end of the main game, do not quit, allow the credits to roll and eventually you will spawn under a tower. Here quickly save your game as a precaution and then hit the "escape" key to bring up the pause menu and enable "Infinite Fly" mode (scroll down with the "Down Arrow" key and use the "C" key to select). In Infinite Fly mode the "C" key is no longer used to jump, instead you can now fly, hold down to gain altitude and let go to float back down to the ground.

Now fly up to the next level of the tower that has three doors/portals (there are two on the top level), move over to the person/memory and turn around to face the doors/portals and enter the door/portal on the left to enter the White Expanse area.

Once in the White Expanse area, enter the building to the right and follow the linear path through the rooms until you enter the room where the security guard earlier blocked your path until you presented him with a signed and stamped pass.

Enter the room next to him (you do not need to talk to anyone or interact with anything, or obtain a new pass) and once you enter the next room beyond the security guard you will get an on screen message "For some reason, you may not Infinite Fly here right now." and the achievement should pop here.

To be safe, try and fly before exiting and you will find that you can only jump in this room and not fly, then exit and the achievement will have popped. See video walkthrough part 7 from the start to end for further information.

***EDIT***
Steam user "Korobooshi" found that the "No Fly Zone" was not in the same location as mentioned, and shown in this guide, for them "the No Fly-Zone was the first forest area. So maybe it's random where you can't fly?"

This is the first time in 5 years, with over 650 views of the guide that anyone has made this claim, so I cannot confirm or deny if there is a random element to this achievement. I can only advise that if it is not where I stated, to check the area mentioned by Korobooshi.

Many thanks for the info Korobooshi.