San Antonio’s zoo, in Breckenridge Park north of downtown, is home to 9000 animals from 750 different species. As well as one of the country's largest endangered-animal collections, it features a mini-train, a carousel and a butterfly garden. All charge a small separate fee, or are included in the Fun Day ticket (adult/child $25/22), which offers a small overall saving.
Note: this isn't a good place to spend a hot summer afternoon. Come early or late, when the animals aren't inside escaping the heat.