There's nothing wrong concrete and steel being visible to the public, provided that is not the only area visible. Many animals prefer to be in their nighthouse when it's cold or rainy, and the zoos may give the animals access. As long as they can see the outdoor area and that the animals have access to it but have chosen to be inside (or have been brought inside temporarily for cleaning/maintenance/enrichment) then the public don't generally have a problem with it.
