The Illusionary Room, also known as Phantom Ganon's Maze, is a location found within The Wind Waker. It is located within Ganon's Tower where Link encounters Phantom Ganon. The name of the maze is never referred to in-game, but the official Wind Waker Soundtrack labels the tracks that plays during this room as the Illusionary Room.
The room is similar to that of the Lost Woods or Woods of Mystery in that there is a specific route that Link must travel through in order to make it through the maze, otherwise he will find himself back at the beginning of the maze. In each room, Link will meet with Phantom Ganon, and after defeating him, Phantom Ganon's Sword will slowly drop to the ground with the hilt of the sword pointing directly to one of the four doors in the room. Link must use the sword as an indication of what room to travel through.
Each of the rooms that Link travels to look identical to each other, but successfully going through the correct pathway will lead you to acquiring the Light Arrows from a treasure chest. At the end of the Illusionary Room maze, you'll encounter the strongest form of Phantom Ganon who can then be defeated using the newly acquired Light Arrows.
The Hilt of Phantom Ganon's Sword pointing to the proper door.