Use W, A, S, and D to move around in the map. Use Turbo mode so that it's not too slow. Really. If you don't have it on turbo mode, it will be extremely slow.
I found the page on the Scratch Wiki titled "Sprite-Based Raycaster Tutorial," and then made this. Try to guess what the shape of the map is. It is possible to glitch out of the map. If this happens, just click the green flag.
