Edited sentence: All these doors lead to the same room, which contains the actual triangular key, plus doors leading to numerous critical locations in the game.First, get into a ship, fly level at speed 4, and fire a bullet.Having done this, you then gain the ability to pick up and drop any object in the entire game, including buildings and illustrative objects.Immediately increase to speed 8 and tap the "pick up" key, and you will pick up your own bullet.In fact, the doors could be opened by a two stage process.Return to the start of the game, pick up your crashed intergalactic spaceship, and you become able to move through doors locked with the triangular key.The Second City was notable for containing one of the most spectacular cheat modes in games of the time: the manual told the player that doors locked with the triangular key could never be opened, because "only the author has the key.The triangle locked doors also provide a way out of rooms in which you are otherwise trapped