Cave of Flames
You travel here to find the Fire Element, the second element you need to forge the Four Sword. This dungeon is covered in lava and fire, and several holes. The main item you acquire here to advance through the dungeon is the Cane of Pacci. The mini-boss you must defeat to gain this item is several Spiny ChuChus. After you defeat the boss, you recieve the Fire Element and a Heart Container to increase your life, then return to the Mountain Minish village to retrieve the fixed Picori Blade, now called the White Sword.
The boss of this dungeon is Gleerok, a fiery turtle-like monster who's weak spot is atop it's back underneath it's rock-hard shell. To get to it's back, you must circle Gleerok until you can hit it with the Cane of Pacci, making it's head and neck drop, making a bridge to it's weak point. Gleerok's main attack is spitting fire at you repeatedly. After the guardian of the Fire Element is defeated, you won't have to worry about this dungeon again.