Doing so requires the use of a few items you might not have in your possession - a Shovel and Bombs - to make a new friend along the way.
If you're looking for more assistance, our Zelda: Link's Awakening walkthrough can help.
How to get to Kanalet Castle
With Bottle Grotto done, you can finally lift the rocks going east out of Mabe Village, allowing you to access Ukuku Prarie.
As you enter, there's a cave to the north where you can grab a Heart Piece, and a warp point east, that's worth activating so you can fast travel around the map.
Head south from here to reach the entrance of the Key Cavern, the third dungeon you need to access next.
Of course, you need the key first. Head south until reach the Pothole Field and a hut, which is Richard's Villa.
Richard will tell you you need to explore the nearby Kanalet Castle. As instructed, make sure you have the Shovel in your possession. It's sold at the Mabe Village shop, and is required to complete this part of the quest, as well as coming in handy for finding Secret Seashell locations across the map. We also advise you purchase some bombs, too, which will come in handy.
Kanalet Castle is to the north-east, in the middle of the map. Follow the linear path right, up and right again, past the enemies, to reach the gate. If you get lost on the way, read the sign posts which will point you in the right direction.
To enter, take an immediate right along the moat, until you find a Monkey. Provided you've been following the trading sequence until this point, you should have some Bananas in your possession. Hand them over and you'll not only receive a Stick, but a bridge going north will form.
Follow the path round to the north of the castle, cut down the bushes and take the staircase that is revealed into Kanalet Castle.
Where to find the five Golden Leaf locations
Within the Kanalet Castle grounds and Castle proper are five Golden Leaf locations. They are as follows:
1. On the east side of the grounds is a bomber that emerges from a series of pits. Attack with your sword just as it's thrown a bomb to damage it until it's defeated, giving up a Golden Leaf.
2. On the west side of the grounds is a bird in a tree. Throw a rock at the tree to cause the bird to attack you. Swipe with your sword to defeat it and receive a Golden Leaf.
3. Inside the castle you'll want to defeat all the enemies in the entrance.
4. Continue exploring the castle - going north, throwing the switch and going upstairs - to find a sub-room below with two cracks in the wall. Use bombs on these (if you don't have any, either go back to the Mabe Village shop, or continue to find some pots with some inside) and defeat the two knights that emerge.
5. Continue exploring the Castle until you arrive outside. Enter the other door, throw a pot at the door above to access a room with a golden knight. Defeat it to receive the final Gold Leaf.
Our Zelda: Link's Awakening walkthrough and guide can help you with the critical path, including the Eagle's Tower and Turtle Rock dungeons. There's plenty to be done on the side, too - including Zelda Link's Awakening Heart Pieces, Zelda Secret Seashells and the Zelda Link's Awakening trading sequence. Finally, there's also the new Zelda Chamber Dungeons feature to unlock and complete.
Now head back to Richard's Villa, will who give you access to a cave. While down there, the left route has a chest containing a Secret Seashell location, while the right has you emerge out at the Pothole Field (which we'd like to think of as Richard's poorly tended back yard).
Swiping the grass away will reveal potholes blocking your path. You can either swipe everything until the path reveals, or go straight to your destination by going right a little, then down to the outer edge, round the outside in an anti-clockwise fashion, and to a patch of grass.
Dig a hole by the feet of the Stone Owl with your Shovel (again, if you haven't got one, go to Mabe Village's shop) to get the key.
Now leave Richard's Villa and insert the key into the dungeon entrance to the north.
To access the Key Cavern, you need to head south of here, anti-clockwise around the Pothole Field, arriving on the east side of the lake next to the dungeon. Use Roc's Feather to traverse the islands across to the entrance.
When you're ready, head inside to begin the Key Cavern dungeon.