Along with a friend, Lindahl founded Colossal Media to resurrect the dying art of hand-painting enormous advertising murals on the sides of buildings. Their company, headquartered in a warehouse in Williamsburg, Brooklyn, has since burgeoned into a $10 million agency that handles the bulk of such ad campaigns in New York and does work in 17 other cities -- braving heights and extreme temperatures to breathe new life into this spectacular, long-neglected art form.