Update: I went back to photograph the building in July of 2020.
The Forest Park Visitors’ Center is an interesting mix of Spanish Revival architecture with a couple bits of other styles. It was originally built as a streetcar shelter, but I suspect the tower was built later or substantially altered, as it does not match the architecture of the rest of the building.
Forest Park Forever’s website says that the tower is the original structure and the rest was replaced after a 1925 fire. Pretty substantial tower for a trolley shelter!