This achievement is awarded for uncovering all the rooms of the facility outside the challenge rooms. Unless you are going for 100% completion, this achievement won't be earned through natural progresion. I would suggest going for this when you are going for the Snappy Threads achievement:
Once you complete chapter 6 Challenge rooms (1-8) you'll receive the Teleporter gadget which combined with the other gadgets will give you unlimited access to the facility. I wouldn't waste time trying to do this before you receive the gadget otherwise you'll just have to come back to areas later on.
Here is a map to compare your own progress. If you're not sure, look for the hard border outlines defining the edge of each area.
This achievement actually popped a few rooms premature for me whilst going through Chapter 5 for the 2nd time.