More Dutch innovation in this edition of The Optimist Daily. Humans are said to have evolved from an ancestor that once swung through the trees to get about, free to move through the environment in almost any direction. But today, that flexibility is gone in a world of stairs and elevators. Enter: Vertical Walking. This human-powered system prototype requires just ten percent of the effort needed to climb stairs, but can easily move a person—even with a handicap—up a vast number of floors. See the video.