Here’s a public artwork for you. In the Palanco subway station in Mexico City an entire staircase leading up from the trains is a piano keyboard. Every footstep plays a note with the ‘music’ composed by the crowds rushing up and down the stairs. It's the work of Mexican artist Remo Saraceni who was into experience art early and who has since taken this idea to the world. You can hear the stairs and see them in action here.