The Saint Louis Science Center does a monthly, nerdy event every month called First Friday. As the name suggests, it’s the first Friday of each month, and each is themed differently. They offer a variety of activities, vendors for fandom merch, and occasionally special guests.
And best of all: it’s free to the public, as is parking. There are select ticketed events they warn, but I didn’t encounter any on this trip to know which to point out.