Certainly not an illusion.
Once upon a time, the terraformers discovered that it was helpful to place the bottom of the building "footings" at some "minus" elevation rather than just plopping objects down on the terrain. Objects which looked just fine in plan view, when seen from ground level had portions of the buildings well above the terrain, particularly when on sloping or hilly grade. I have screenies of hillside concrete bunkers and and other buildings which only had about 1/2 of their footings in the ground, the other half "floating" above the ground. Cantilever construction is possible, but expensive, and certainly was not what was intended. There are likely still examples which can be found, but to the terraformers' credit, the problem was "fixed" by lowering the buildings. I'd doubt that any newer terrain would continue to show similar examples.
"Fixed" Condition. The whole tent is there, the appropriate parts are just below grade.
EDIT
Shown is the actual condition of the revetments at F-6. The first screenie was grabbed from "below grade" not AT grade as is the above. These revetments are actually well sunken into the surrounding terrain. The characterization that there is a "bug" is likely appropriate.
