San Diego, California
This ones a no-brainer. It goes without saying that the city home to the worlds most famous zoo is on this list, and there is no denying that the San Diego zoo is one of the greatest zoos out there. Half of the zoo is enclosed within a natural tropical rainforest environment with countless species in (mostly) high quality exhibit areas. What other zoo can you experience that? The Safari Park also is equally brilliant with its multi-acre field exhibits and and up close encounters. This duo of zoological powerhouses alone could make San Diego the premiere zoological destination. SeaWorld San Diego, as controversial as it may be is also an extremely popular park and when it comes to rare species, is a must see for many zoo enthusiasts. Where else can you find killer whales, pilot whales, emperor penguins and pacific walruses all at the same park, not to mention some of the only Guadalupe fur seals anywhere in captivity. Other smaller locations include the hidden gems of the Living Coast Discovery Center and Birch Aquarium in Chula Vista and La Jolla respectively. Overall, San Diego is of course a fantastic city for zoo nerds for the two big parks alone and the rest of the additional facilities are just the cherry on top of it all.