This is the COOLEST place in the world (I'm not biased). You have to come here to see the magic! It's a giant warehouse full to the brim with all sorts of different playgrounds, jungle gyms, caves, ball pits, slides, a skate park, art center, circus shows, a ferris wheel, a shoelace factory, and much, much more!! It's straight out of a storybook.
Best zoo ever (again, not biased)!!! But also, IT'S FREE!!!! And the exhibits are so extensive, it's hard to believe you entered for free. Our favorite exhibits there (if you're on a time crunch): River's Edge, Penguin and Puffin Coast, Polar Bear Point, and Fragile Forest. Also, this zoo is located in Forest Park, which brings us to our next recommendation...
Visit "The Heart of St. Louis," our 1300-acre urban park! You can walk around and admire the greenery and water features, or you can visit one of its numerous attractions (many of them free). The Saint Louis Zoo, The Muny (outdoor amphitheater), Saint Louis Art Museum, Saint Louis Science Center, and Missouri History Museum are its five main attractions. You can also pay a visit to the Jewel Box (a greenhouse), Turtle Park (sculpture park made of turtles!!), the Boathouse (a restaurant and boat rental facility- take a paddle boat out on the lake), World's Fair Pavilion (open air pavilion with great views of Forest Park), and many, many others.
Take a tour of Anheuser-Busch's oldest brewery site, in the city where it was founded in 1852. Learn about the world's largest brewing company while sipping on free beer. Or, if micro breweries and craft beer are more your thing, St. Louis has PLENTY of those too! Check out: 4 Hands Brewing Company, Urban Chestnut Brewing Company, Schlafly, Morgan Street Brewery, Lafayette Square's Square One Brewery, Trailhead Brewing Company, and so many more.
And of course, what would a list of St. Louis attractions be without the Arch? Even if you don't want to go up into it, it's worth seeing in person, with an informative museum in its basement, and it's situated right next to the riverfront if you'd like to explore the area.