Temperate zoos show their animals indoors for part of the year, and build great indoor spaces for primates, birds or crocodiles. However, tropical carnivores and hoofed animals usually have only functionally designed 'dens' or 'stalls'. Which zoos went beyond this, and make large and naturalistic indoor spaces for those animals? I am not talking about all-indoor exhibits, like found in some American zoos, but indoor part of the indoor-outdoor complex. Few examples: Zurich zoo recently build a very good house for their giraffes and rhinos. For some reason, elephants and hippos often get good indoor exhibits, but not rhinos: Milwaukee has indoor exhibits for tigers, and also lions and spotted hyenas in rotation. Spacious and naturalistic, although almost all hard surface: Lions and tigers in Wuppertal have indoor exhibits with a quality which I liked very much. It is visually one with the outdoors. You wander between rocks, and suddenly don't look at the outdoor enclosure anymore, but at a similar indoor exhibit.