I'll second Amos's recommendation(s) of the San Diego Zoo, and especially the Wild Animal Park a few miles out of town. The open-air train circles the property and one watches the animal herds roam around, from cheetahs, lions, elephants, springbok, antelope, hippos and rhinoceros, exotic goats and sheep. And more. It is quite a place. Oh, and don't miss the butterfly pavilion.