Edgar Mueller spent five days, working 12 hours a day, to create the 250 square metre image of the crevasse, which, viewed from the correct angle, appears to be 3D. He then persuaded passers-by to complete the illusion by pretending the gaping hole was real. “I wanted to play with positives and negatives to encourage people to think twice about everything they see,” he said. “It was a very scary scene, but when people saw it they had great fun playing on it and pretending to fall into the earth. I like to think that later when they returned home, they might reflect more on what a frightening scenario it was and say, ‘Wow, that was actually pretty scary!'”