When you open the page, you're standing in a 3D park; use WASD to walk and the mouse to rotate your view. At first, there's nothing strange—it's just a normal park. Then you start walking faster. The faster you walk, the more the park seems to be playing tricks on your eyes. Because in this world, the speed of light isn’t 300,000 kilometers per second—it’s 5 km/h, roughly the speed of a brisk walk. So those Einsteinian effects that are usually hidden at extreme speeds suddenly happen the moment you press W. The world in front of you turns blue, the world behind you turns red, distances ahead shrink, and your wristwatch and the world’s clock no longer sync up.