WHATS BEHIND THE GREEN DOOR

Looking a bit like a Roman Small-house - this is a picture of an old Municiple Electricity Department (MED) substation.  There must be a 100 of these small buildings scattered throughout Christchurch and to the best of my knowledge not one of them got bowled in the Christchurch Seismic Storm even though about 60% of the inner city was either flattened or has been since by bulldozer ( ot whatevere they're called nowadays.
There must be a building lesson here somewhere ?? I think I know what it is - Do you ?? virtual choci fish for right answer !!
rgds poo