Glitched Palace

From Glitches

From the game The Legend of Zelda 2: The Adventure of Link for the NES.

Go to any palace that has blocks that fall and wait until they pile up to the ceiling. Get Link on top of the pile so that he's offscreen, then use the Fairy spell. Press left or right and Link will fall and land on top of the palace. Jump up off the screen, activate the Fairy spell again, and press left or right. Link will fall and land in a strange palace that is the same color of whatever palace you were just in, but has a layout and enemies identical to that of the first palace. When you leave, you'll be near the palace you actually entered.

Taken with permission from Flying Omelette.