Super Mario RPG took Mario from the boring two-dimensional guy he'd been for... well, for his whole 'life' and gave him the ability to move in some kind of pseudo three-dimensional space, pretty neat.

But, just for fun, there are references to old Mario stuff all over the place, like in Booster's Tower. Go far enough in, and you'll find this room.

Pretty bland, right? But those curtains... Walk back behind them and you'll hear some classic music start to play, and when you step out...

You can't really do much like that, though, and the effect wears off as soon as you try to leave the room. You should note, though, that you can only do this once. Save the game after you do it and you won't be able to do it again unless you start the whole game over again.