Paint Louis, which takes place here over Labor Day weekend, is a big international gathering of graffiti artists, taggers, DJs and hip-hoppers. It's arguably the largest single graffiti event in the world, covering a 2 mile / 3.2 km stretch of the Mississippi River floodwall south of the Arch, all sanctioned by the city. The result is considered the longest mural in existence by the Guinness Book of World Records. https://en.wikipedia.org/wiki/Paint_Louis
I went for a look late yesterday afternoon and things were just getting started. It's supposed to rain most of today and I don't know how it will affect the schedule. https://www.facebook.com/PaintLouis/ I'll be back when the weather permits.