Mario Kart The Legend of Zelda: A Link to the Past Final Fantasy VII Contra 
Answer: The Legend of Zelda: A Link to the Past
In 1990, Nintendo held a contest through their now retired magazine Nintendo Power with a grand prize of a cameo appearance in a Legend of Zelda game. One Chris Houlihan won by meeting the contest requirements first via mailing a picture of himself engaging the elusive Warmech boss in the game Final Fantasy. While we’re sure Chris was expecting to be a non-player character or even a painting on the wall of a castle, his cameo was radically more obscure. The developers of The Legend of Zelda: A Link to the Past, turned Houlihan’s cameo into part of a game-crash prevention trap in the form of a room that is not accessible during normal play.
So how obscure is the room? There are only about five ways you can end up in the room and none of them involve walking in the front door: the most practical (if you can call it that) method to get into the room is to wear the high speed Pegasus Boots and perform a crazy speed run from the doors of the castle Sanctuary to the secret entrance to the Hyrule Dungeon. Perform it fast enough and with no pauses, and instead of tumbling into the dungeon you’ll confuse the game’s algorithms and end up tumbling into the secret room.
What’s in the room? 45 blue rupees and a telepathy tile on the back wall. Touch the wall and you hear “My name is Chris Houlihan. This is my top secret room. Keep it between us, okay?” Upon exiting the room, you find yourself standing in front of Link’s house where the game begins.
The room is so obscure, in fact, that it wasn’t until people started playing the game in emulation and poking around inside the game’s ROM that it became widely known. Sadly for Chris, this was about a decade and a half too late for anything remotely resembling worthwhile bragging rights to his Nintendo Power reading buddies.
Image courtesy of Nintendo.