How hard could a maze with no walls be? Extremely hard, if the walls only appear once you start moving, as in the so-called Quantum Maze, by Jonathan Welton. The goal is to move from the green circle, touch both of the blue circles, and end at the red circle. But with every move, walls appear ahead and to the sides of you. It’s very devilish and maddening — like you’re playing a game of Quoridor against Schrodinger’s cat. I still haven’t been able to do it.