Of all the cheats and secrets tucked away in GoldenEye 007, we never suspected Rare's N64 classic harboured a fully functioning ZX Spectrum 48k emulator.
Rare began a coding experiment to see if the N64 could support a Spectrum emulator, even embedding old-school Rare games Sabre Wulf, Jetpac and more in the code. Clearly the experiment worked, but it was never removed from the final retail code and remains to this day.
Don't go booting up the game and trying to play some Knight Lore though: while the emulator is fully functional and resides in every retail GoldenEye cart, Rare rendered it inaccessible and inoperable. For shame.