Described by Jojo Klein:
Starting at the cablecar station of the 'Nebelhornbahn' in the valley, the goal is to clap the cross at the top of the Rubihorn and going all the way back to the cablecar station.
There is no route or way predetermined. Just follow the fastest track you can find. The only importance is to start at the Nebelhornbahn in the valley, clapping the cross at the top of the Rubihorn and running back to the start.
Here in Oberstdorf, we call this challenge 'Rock the Rubi'.