I went to the Cahokia Mounds pretty much as a last minute visit before heading out of Saint Louis, I just saw the sign and decided to go there. I am glad I did. I had no idea this even existed but am glad I took the time to learn about it. It was a very intresting site, did not take long to go through but was very informative. I am generally not intrested in archeological stuff but even I found it intresting. I recommend taking an hour out of your day as you pass by and visit it. It is worth the look and it's free (although you can spend money in thier gift shop, or through donations if you want)