Dutch designer Joris Laarman will build a bridge in 2017 by wheeling a robot to the brink of a canal in Amsterdam. He will push an “on” button and then walk away. When he returns in two months, the Netherlands will have a new, one-of-a-kind bridge, 3-D printed in a steel arc over the waters. This isn’t some proof-of-concept, either: when it’s done, it will be as strong and as any other bridge. People will be able to walk back and forth over it for decades.