A Slower Speed of Light is a first-person prototype game where players move around in 3D space collecting orbs that gradually decrease the speed of light. Custom-built, open-source relativistic graphics code allows the speed of light in the game to approach the player's maximum walking speed. The visual effects of special relativity gradually become apparent to the player, increasing the complexity of the gameplay. These effects, rendered in real time with vertex accuracy, include the Doppler effect (visible red and blue shifts and infrared and ultraviolet shifts into the visible spectrum); spotlight effect (increased brightness in the direction of travel); time dilation (differences in the perception of the passage of time by the player and the outside world); Lorentz transformation (curvature of space at near-light speeds); and the run-time effect (the ability to see objects as they were in the past, thanks to the time it took the light to travel). Players can share their skill and game experience via Twitter. Slower Speed of Light game combines accessible gameplay and fantasy setting with theoretical and computational physics exploration to deliver a fun and rich pedagogical experience.