The world of Koholint Island is decently large, with plenty of different areas for you to explore. Many of these are locked off at first and require you to get additional items to continue. Following the completion of the third dungeon, you will eventually need to make your way to the Animal Village, which you may have trouble finding at first. This is because the entrance to that part of the map is hidden, but this guide will tell you exactly where to go.
By this point of the game, you will have already traveled to and opened up Kanalet Castle, so that is a good starting point to go to. Once you reach this area, head directly south for a bit and when you see a series of trees like in the image above, head to the east a bit.
As you can also see in the image above, there is a lone bush on the right end of this stretch of trees just waiting to be cut down. Do exactly that to reveal a hidden staircase as seen in the below image and go right down it.
Once you are in this underground area, you must run to the right with your Pegasus Boots to destroy a block in the way that can only be destroyed with that type of charge. However, there are Piranhas in the water you have to either avoid or destroy as well, or you will certainly take damage.
Now take the stairs on the other side to surface and head south and the Animal Village will eventually be on your right as you move further south, which you will have to visit to continue your journey.