Taronga Zoo is the city zoo of Sydney, officially opened on October 7th, 1916 and is home to over 26000 animals on 287 hectares, making it one of the largest of its kind.
Taronga Zoo is an amazing place to visit. You can easily make a day out of it. Taronga Zoo is approximately 12 minutes by ferry from Circular Quay and the CBD. (Ferries depart Circular Quay, every quarter past and quarter to the hour). The zoo is on Bradley's Head Road, Mosman, Sydney. and has both street parking or for a small fee of approximately $10, you can park in the car park. It's also accessible by bus.
For a fun day out with the kids, or by yourself or even for a great photo opportunity, I highly recommend Taronga Zoo.