DK64 - Test Room.

A hidden testing room can be accessed by using a code in Snide's HQ. After collecting all the Blueprints, go to any Snide's HQ in any level and bring up the Bonus Menu. Highlight any of the mini-games, then press and hold B and quickly press A. If you did it exactly right, you won't be taken to the mini-game, but instead a strange room. The room has no music, three pedestals, a yellow balloon, and a motionless clone of Donkey Kong. There is no escape from this room: if you walk off into the dark space beyond the borders, you will appear to exit the room but will reappear back inside of it again. Pressing Start also does nothing, so exiting the level is impossible without turning the game off.