If you plan to go out for the night, the city of St. Louis offers a variety of things to do after school, if you consider them. When it comes to the party scene, however, most parties happen off campus, and it is best to go elsewhere or to another neighboring campus like Washington University or St. Louis University. These places are near the most active clubs and bars that usually require a "classy and casual" dress code if you plan to go to one of the more "sophisticated" clubs.
It is possible to hear about a house party through word of mouth, but it all depends on the kind of crowd one prefers. There are both non-partiers and partiers on campus. Bars can be found as close as two blocks from campus, like Weber's Front Row, or as far away as Washington Avenue in downtown St. Louis. It also depends on what kind of cash you have, with regular beer being about $2 and upscale mixed concoctions for $10 each. For a regular night on the town, or for the under-21 crowd, there are plenty of movie theaters, performance theaters, shopping centers, local landmarks, tourism areas, museums, and parks to check out, provided you have some cash on you.