Madrid Zoo is famous for having a wealth of concrete in many of the older, outdated exhibits, but I've heard that it is tremendously expensive and time-consuming to chisel/bulldoze cement into oblivion. Has the zoo attempted to plant vines and other green plants to hang down and obscure the unnatural appearance of some of the enclosures, or has there been an attempt to modernize a few of the oldest exhibits? There is certainly a stark contrast between the zoo in Madrid and the African extravaganza (complete with mowed lawns) in Valencia.
Interesting, if rather archaic, enclosure design. One of the Lions(female) from here went to Port Lympne a year or so ago. I believe the Madrid Lions are an 'offshoot' of the Rabat Strain- related to them but a slightly seperate line.