On Lake Geneva in the Canton of Vaud, performances by dancers and musicians are held annually under the open sky in the medieval town of St. Prex. A covered venue for the event was installed for the first time in 2012. This roof consists of a hemispherical  balloon  with  an  inner  ring  at  its  bottom edge  to  absorb  the  deflection  forces  from  the  balloon. The balloon itself is fixed to the inner ring at forty-eight  attachment  points.  The  hemisphere  is attached at six load transmission points to the truss-like  stage  ring  at  a  height  of  about  twelve  meters, which  corresponds  to  roughly  half  its  diameter. The ring, in turn, rests on three groups of columns that  are  hinged  to  individual  concrete  foundations. Three load transmission points transmit only compressive forces, while the remaining three can be  locked  in  place  and  also  transmit  tensile  forces. The  stage  ring  is  tilted  about  eight  degrees  from the horizontal. The higher part covers the spectator seating and the lower part covers the stage.

When filled with helium, the balloon and its inner ring can float above the stage ring. The hemisphere will ascend into the sky while anchored by three pairs of cables, whose upper ends are fixed to the load transmission points of the balloon’s inner ring. To be able to regulate the position of the balloon  in  space  as  desired,  one  cable  from  each  pair is secured vertically and the other diagonally. This permits adjustments in all six degrees of freedom.

The  design  of  the  helium  balloon  and  the precise constraints it mandated were developed in consultation  with  a  firm  that  specializes  in  constructing large balloons.