The crowds look down from above and are fragranced by a rising incense of engine fumes. The point is to thrill the audience, not to scare them. The riders begin by circling the floor, then up on to a ramp, and finally they are riding perpendicular to the wall, arms outstretched, rising and dipping, sometimes high enough to leave tyre marks at the very top, prompting squeals from the crowd. For superstitious reasons, they only ever travel in an anti-clockwise direction. They get so close you could reach out and touch them, make some sort of brief physical connection with that speeding miracle of guts and grace and centrifugal force.
(via The Scotsman)
A longer video with less noise and more stunts…
…and The Wall itself.