Dungeon 3

 Go up until you encounter some Zols. If you picked up the White Sword already, you'll notice that it kills them, rather than splitting them into two Gels. Neato. Anyway, collect the Key and continue going up.
These demon-looking guys are Vires. Like Zols, they split into two enemies if not attacked with a strong enough weapon. They will split into two Red Keese if not attacked with a Bomb, Silver Arrow or Magic Sword. It's a waste of Bombs to attack them, so just attack with your sword. After slaying them both (and their Keese offspring), you'll get another Key.
Keep going up until you reach this apparent dead end. Set a Bomb here and watch a path open itself up for you.
These guys are Darknuts. They are immune to head-on attacks, so fighting them is a pain. Luckily, you can avoid fighting these ones. Just go down the steps.
Yay, it's a Raft! This'll come in handy after you're finished with this Dungeon.
Return to the room just above the first room (the one with Zols in it). Go right, then head down. Follow the path until you reach this subtle hint. Drop a Bomb here.
Yay, another Key!
Go back to the room just left of where you found that key (you'll have to go down and circle your way back. Now go right, through the locked door in the room where you just found the Key. You'll find the Map here.
From the Map room, go down one room to find a room filled with attacking statues and Blue Goriyas. Defeat the Goriyas and you'll net yourself a shiny Magic Boomerang to replace your Wooden Boomerang. It's faster and flies farther than the old model.
Now just keep going north. At this point, you'll have to push this block to open the door.
When you reach this old man, just bomb the left wall to continue on your way.
Keep following the path. When you reach this room, you are only one room away from the boss room, so be prepared.
It's Manhandla! Depending on how you fight it, Manhandla can be very easy, or very hard. If you attack with your sword, each head you slice off will cause it to go faster and faster. It's much easier to use Bombs. A single well-placed Bomb will put Manhandla out of comission permanently.
A winner is you.