Der B is the zoo fan in our house. Every time he sees some exotic animal on the television, he suggests that we get a "______" door, along the lines of a doggy door. This gets awkward when the animal in question is larger than the kitchen door itself.
We've taken the grandlads (and their parents) to the zoos in Philly and DC. DC is an embarassment, not at all well thought out and grungy. Philly is better. Sorta.
I liked the zoo in Berlin, an interesting place. Their area for the mountain goats was particularly good, a craggy expanse of nearly vertical rocks that gave the goats a good place to play.
San Diego is, of course, world class.
The Aquarium of the Pacific, in Long Beach, is a wonderful place, with playful sea lions, otters, and many exotic creatures of the deep.