Via EnglishRussia.com comes this terrific project in Lvov City, Ukraine in which a massive crossword puzzle was painted on the side of a 100 ft high apartment building.
Questions for the puzzle can be found in various locations around the city, on monuments, theaters, fountains, etc. Each evening people meet at the building to check their answers. The way this works is that in the day time the puzzle is empty. But at night special florescent lights come on, and the answers in the puzzle become visible.