There seems to be a growing number of for-profit street events that travel from city to city. The latest one is Slide The City. The organizers put up a four-block long water slide down Market Street and sold tickets for a fair amount of money. A tube or inflatable slide was required. It you bought a three-slide ticket they threw one into the deal.
Downtown St. Louis doesn't have much slope so no one got up a lot of speed. Still, people seemed to be having fun. Lots more where these pictures came from.