After you defeat Broken Joe in the underground ruins, you emerge from the cave to a new area.

Explore the Area

You are now in another section of the underground cave.

If you don't want a Big Heart, go east until you find a passageway to the north, and go north at that passageway, and skip to the next paragraph. If you do want a Big Heart, go east until you reach a dead end, then go north at the nearby passageway. When the path splits, go left, then at the next split, go north, and go down the stairs to find the Big Heart. Go back up the stairs, then go east and follow the path until it splits. Go west at the split, then at the next split go south. From there, go west until you're in the area where you first arrived, and go north.

Keep going north, then when the path splits, go east to the next room. Then go northeast, then east until you can go north. The north passageway will take you to a new room.

Go west, and when you approach the big rock, there will be some dialogue. Then go north past the big rock, then go east, then finally go north to reach the second cave of chapter 6.