CiSRA Puzzle Competition 2013 - Solutions

3D. On Reflection

Each of the yellow squares show a pair of lines separated by an angle of 45°. The initial deductions which help to make progress are that the lines need to be extended, and that at each brightly coloured square, a reflection of some kind occurs.

It happens that if yellow squares (as shown) impart a 45° reflection, green squares 90°, and cyan squares 135°, then all of those squares can be visited by a continuous looping beam of light, as follows:

From this completed grid, words can now be read from the pale yellow regions:

The answer to the phrase KILLED MEDUSA, and the solution to the puzzle, is PERSEUS. Perseus is fabled to have slain the gorgon Medusa, avoiding her petrifying gaze by only looking at her reflection on his mirrored shield.