I have been to zoos all over the country and I can say without reservation the St. Louis Zoo is my favorite. It is located in Forest Park--St. Louis's Central Park. Admission is free--however, some exhibits inside are not. The park is large enough that just seeing the free parts of the zoo will take all day however. The front entrance of the zoo (look for the big "zoo" stone sculpture) has free parking along the street leading up to it. Like most zoos, the best time to go is weekdays during spring and fall, the earlier the better. When you first go in to the right will be Historic Hill--the oldest part of the zoo and my favorite. The buildings there were built during the twenties and are exquisite. Be prepared to walk up steep hills, however. Also part of this section is the walk through a bird cage--part of the 1904 World's Fair. To the right of this section is Red Rocks, which includes the big cats. Be sure and walk over the bridge over to the tigers area. To the left of the bird cage is the Jungle of the Apes. Very close-up viewing of the primates housed here is available, as well as seeing them in their natural settings. Be sure and look for the naked ape.
The lakeside café has the nicest setting of any zoo café I've been to--though the prices and selection is par for the course. Picnic lunches are allowed and this makes the zoo a welcome stop in summer, as it is air-conditioned in the inside section. The rest of the year I recommend sitting the perimeter section, on the outside. Very lovely. Wild birds, including peacocks, often come here looking for bread crumbs.
Rivers Edge is the newest part of the zoo, housing the elephants, rhinos, and hippos. Because it is laid out to give you a feel of really being in the wild, expect to do a LOT of walking here. It is very well done and interesting, but will take up a large part of your vist by itself. If you have to skip something, this would be it. Also, the Living World is geared more to school groups and while interesting, can easily be by-passed. Penguin and Puffin Coast is due to open on Memorial Day and looks to be well worth a visit. These parts of the zoo require admission: Children's Zoo--$4.00 each, but free from 9am-10am, Insectarium--$2.00 each, Train--$4.00, and Sea Lion Show--$3.00 each. A Safari Pass can bought at the entrance for $10.00 each and will give you unlimited visits to each of the paid attractions for that day.