Earth Hour 2012

Earth Hour has grown since its start in 2007 to now include observances in 147 countries and over 5000 cities. For one hour, lights are switched off on the last Saturday in March - leading to stunning pictures especially when famous landmarks are concerned. The linked contribution by the Boston Big Picture site has 25 shots of the event, with the added bonus that by clicking these shots you can convert them from lights on to off and vice versa. The illustrating image above I created myself as an animated gif from two Chinese Wall shots (credit: Lintao Zhang/Getty Images).