Here is the full list of all 19 The Backroom Project achievements.
Spend 2 hours in one level of the Backrooms at once
Find the Hound of the Pipe Dreams
Enter the Pipe Dreams level
Meet with an entity on Level !
Walk downstairs multiple times on Level !
Pick up a Key on Level !
Enter Level !
Find a Duller in the Backrooms
Enter the Habitable Zone
Find a Corpse in the Backrooms
Find the Entity in the Lobby
Meet with a friend in the Backrooms
Die in the Backrooms
Fall down in the Pitfalls
Find the Pitfalls
Accept the offer and get sent into the Backrooms
Try to run in the Siren Facility
Escape the Backrooms