Elephant and Rhino House, London Zoo. Sir Hugh Casson 1962-65
There's currently a sign outside the entrance to the building saying that the elephants and rhinos have been moved out because it no longer fits in with the current thinking on welfare (which seems to favour enclosures more imitative of the animals' natural habitats) although you'll find that it's not vacant, there being two large molty (or are they mangey?) camels inside along with a lot of bearded pigs and an armadillo.
But assuming that the building wasn't actually doing the elephants any harm I think the zoo should consider standing by it - and it's original purpose - because there's something truly magical about seeing animals here (even pigs) that is unique and deserves a serious attempt at re-assimilation.
If the problem is also one of public perception (as hinted at in Keith Miller's 2002 Telegraph article.) then the solution should perhaps be more one of public information than architectural intervention (although a spruce up of the interior a la Royal Festival Hall would be a welcome show of faith).