6 towers placed hundreds of meters apart. At a central location, the players can trigger cannons in each tower. Because of the speed of sound some locations will have the sound of the cannons arrive simultaneously.  

Originally an idea for a russian festival, but any land art spot would be an amazing location for this.

It would be amazing to physically experience the speed of sound by moving around in a landscape. Walking closer to one tower would bring the explosions out of phase. But also the shape of the landscape will alter how the sound moves around.

The exact timing of the cannon shots could easily be achieved by using realtime from gps-receivers.