The Bonn Vert Ramp
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...