you have to A) rescue the cute guy after beating the fourth dungeon of the dark world, and B) have the master sword. go to the blacksmiths house and talk to them. they will temper ur sword for ten...
in the dark world, there is a crack in the wall on the perimed. you cant use an ordinary bomb though. you know that sick littel elefant in the bomb shop? you have to beat the sixth castle in the dark...
You need to beat both games in the game pak (The legend of Zelda a link to the past and The legend of Zelda four swords). That's the only way to get in there unless you want to hack into your own...