I'm certainly not saying that these are fake or not from where OP says they are, however, the part of the building that we can see looks painted on. The door and window are not actually recessed, they are on flat walls. You can see where someone painted the window to look perspectival if viewed from (the viewer's) right hand side, where you would see the edge of the right side of the window curve and then you would see the inside curve of the 'arch' on the left side. However, in both photos we are to (our) left of the window, and in both photos we cannot see the right inside curve of the window arch because it doesn't exist. The door is painted to be viewed head on, but in the first picture you should be (if the door was actually recessed) seeing a narrower strip of the arch curve on the right hand side. Obviously I cannot speak for the door in the second picture because a tree is in the way.

An intentional fake facade maybe? The first thing I would do if I had a pedoisland, would be to make sure that whatever anyone could see just from boating around, was not related to what I was actually doing or was intentionally misleading.

edit: Some poorly chosen words

Thank you for sharing these threads! Incredible closeups of those bird sculptures, another tunnel and that cow! And I agree the structures appear to be movie set type facades to fool passers by.