The Cahokia Mounds State Historic Site is located across the river from modern day St. Louis, and is an old Native American town that has been there before any city ever was. Now, it is a beautiful set of trails that you can go and explore. Whether you choose to go by yourself, on a guided tour, or even an IPod tour, it is a great experience to understand how the Native Americans once lived. Once you are done, stop by the Interpretive Center where there are tons of stations that will explain culture, buildings, life in the city, and more. You can even stop by the diner and grab a bite to eat on your way out.