The Leidenfrost Maze was designed and built by University of Bath physics undergraduate students Carmen Cheng and Matthew Guy to demonstrate the self-propulsion of Leidenfrost droplets. The maze, built out of aluminium blocks, demonstrates how water droplets can be made to move in different directions when they come into contact with a heated metal surface.
This occurs when a liquid drop comes in contact with a hot surface that produces an insulating layer of vapour that keeps the drop from evaporating rapidly. This layer also allows the drop to glide effortlessly over the surface. If you replace a smooth surface with asymmetrical teeth, the drop will move rapidly in one direction. By using the uneven surfaces to accelerate liquid drops, the team make the drops move uphill and even follow a predetermined path through a maze.