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