The puzzle is hidden in the illustration for the puzzle, townhall.png. I just opened the PNG in a text editor and inserted some clues, and then messed around a little more so the image would look more corrupt and the clues would stick out more when you found them in the image data. They say:
The correct extensions for these filenames would be SIN, GLE, PLA, and YER, so the answer is SINGLE PLAYER.