Berlin, Germany, 1939-1945
I created a website where people can leave their mobile phone number. The idea is that when the number of people is large enough, a SMS instruction is sent to all of them simultaneously by the server. When they receive it, people have to perform the instructions. The instructions are simple ones, like raising an arm, but the effect is amplified by the fact that many people do it in the same place, at the same time, as in a symphonic orchestra.