Make sure to be banjo alone to do this. Go to the lava place in Halfire Peaks, then go to the place with the hot water. Use banjo's Z+C-down move to be in his backpack. Go down in the water and go in the small hole down there. Keep running in the wall and then jump into the wall a few times. Get out of your backpack. You can now travel around in the water as if you were on land! Note: To get back on shore, find the pathway that leads up and onto land.