This article says "The Halfpipe is existing since more then 27 years now at the same location, Rheinaue, Bonn. So it is the oldest continuous halfpipe spot in Germany."
Incidentally, I once lived in Bonn, Germany for a few months in 2001 for my first academic postdoc (at the Max Planck Institute there) as a mathematician. When I was there a large temporary vert ramp mysteriously appeared right around the corner from the Institute. Unfortunately, I don't have any pictures...