The anonymous Spanish art collective Luzinterruptus like to use light as a raw material and the dark as their canvas to carry out urban interventions in public spaces and draw attention to problems in the city that often go unnoticed by people as well as the authorities.
Their most recent intervention, Walking in the Rain, took place on October 26th, the first day of rain after a completely dry summer in Madrid. In celebration of the rain and, thus, cleaner more breathable air, Luzinterruptus placed 50 illuminated rainboots in Parque del Oeste for a 10-hour period as encouragement to others to put on their own boots and walk happily through the rain.
You may also want to take a look at their two other recent interventions: Under Nuclear Threat and Public Art that you Fancy Touching.