The San Diego Zoo may be the best-known zoo in America, but you're also going to pay $42 a head for the privilege of enjoying it. Not only is the Saint Louis Zoo as impressive as San Diego's facility, admission to our zoo is completely free. F-R-E-E. Yet despite the free-ness, the Saint Louis Zoo is constantly reinventing itself, such as the opening this summer of the fantastic Sea Lion Sound that takes you under the water with these fun-loving aquatic mammals. But, truth be told, it's the older features at the zoo — the bear pits dating back to the 1920s and the flight cage installed for the 1904 World's Fair — that keep us coming back year after year. That's right, not only will the zoo's animals entertain your out-of-town friends, but you can also use the zoo's architecture to bore them with St. Louis history!