Here is another ambient ad from South Korea. I like OOH that gradually changes with time. The disadvantage is that people who see the advert before the transformation takes place don't get to see the full effect of the message, but it's usually pretty impressive.
To raise awareness on "Bear Farming," the practice of caging bears to extract their gall bladders for medicine, this floor poster was made. Adhesive tape would slowly pick up passerby's foot prints, exposing the caged existences these bears live in.