Everything comes to a complete stand still. No cars, no shopping, no noise, no polluting smells (see graph below, air pollution drops by a factor 100), no nothing. I live right on the sea shore just north of Tel Aviv, very close to the busiest highway crossing of Israel. It is magical to see human society grind to a halt, and you can almost feel the energy of a few million people near by reflecting on what contributions they have made over the past year. The sun setting and the only sounds remaining are those of the sea, the wind, and the birds. This is not your average car-free day, it is really about letting nature taking back over.
As designers, we need more of these moments that enable us to get rid of the clutter in our minds.