Parkour runners do a move where they run up walls and back down. This is a variation of that.
The wall would actually be a chimney opened on one half that would rise perpendicular to the ground. The ground would slope up to this wall allowing the runner a smooth transition from horizontal to vertical as they tried to see how high up the chimney they could run.
The trick would be to know when you're going to lose that momentum carrying you around the chimney so you could turn and run back down staying on your feet. If you misjudged, you would just stall out and fall flat on your back. The curving of the wall into a chimney is to create centrifugal force that the runner can tap to run higher up the wall.
So to be clear, you'd run up to this thing in a vertical position, transition to horizontal as you ran up the wall and if you did it right, turn around facing back down and run back down transitioning again to vertical.
There would be numbered lines on the wall showing how high you got.
Based on RayfordSteele's story about an empty pool sort of shaped like this in which the kids would run at various angles.-- doctorremulac3, Aug 15 2015random, halfbakery