Anyone who ever owned a Nintendo GameCube should remember just how good F-Zero GX was. It may be one of my favourite racing games of all time. That game was released almost 10 years ago, but it was only discovered today that the arcade version of F-Zero GX, F-Zero AX, was completely hidden in that game's code all along. Amazing.
If you're interested in trying to make it work, you'll need a copy of the game, obviously, a GameCube, and an Action Replay device. You'll have to enter a series of pretty intensive codes which you can find here.
Personally, It's enough for me to know that it simply exists, and that something like this could have existed for so long without someone noticing it! I remember actually buying a copy of F-Zero GX day one in Japan, and I remember playing the arcade. It's insane that the two games were linked together on the same disc for all those years without anyone knowing. Incredible.