After you rescue Baboo, you discover the frequency for Nav-Com to find Dr. J's location, and proceed to Bellcola.

Visit Bellcola

Go north and get out at the dock, then go north and walk onto the house to enter the village of Bellcola. Talk to everyone in the village, then talk to the guard at the hut. Go in and talk to the village chief, and there will be a cutscene. Say Yes when asked if you promise to keep the secret. He says you need Peter's help.

After the cutscene, go south to exit the village, then go west to find Peter. (If Peter isn't there, you need to talk to the village chief as described above.) Talk to Peter and there will be a cutscene.

Find a Gift for Peter

Peter won't tell you anything unless you give him a gift, so go east and enter Sub-C. After a brief cutscene, go east until you can't go farther east, then go south. Eventually, you find some dark waves. Go onto them and press B to dive. Go north and press B to dive into the northern waves, then go north and push into the west wall until you find the hidden tunnel. Move Sub-C into the dock, then get out and go up the stairs. Go north into the hut and talk to Hook, the fisherman, and say Yes to get a worm.

Give Peter the Gift

Exit the hut and go south to Sub-C. Go in, then after the cutscene, push east through the wall until you come out on the other side. Go south and dive into the dark waves, then go south and dive into the southern waves. From there, go north, then west to the dock, and get out.

Go west to Peter and talk to him. You will automatically give him the worm. He gives you the following clue: Do Me So Far, Do Me?

Get back in Sub-C and go east until you can't go farther east, then go south. Dive at the dark waves, then go north and press B to dive into the northern waves, then go north and push into the west wall until you find the hidden tunnel. Move Sub-C into the dock, then get out and go up the stairs.

This time, go south on the grassy path until you can't go farther south, then go west, then north until you can't go farther north. Then go west and you will enter a hidden tunnel in the mountains. Go to the northwest end of the path and go west to enter a new part of the tunnel. Go to the northwest end again, and go north to go outside. Enter the nearby building. If there is a mountain in the way, you went the wrong way. Go south into the mountain tunnel, south to the previous part of the tunnel, then go west, not north. Go through the tunnel to reach the building.

Play the Organ

If you step on the leftmost key of the organ, it says "Do". You may have heard of "Do Re Mi Fa So La Ti Do". The keys on the organ correspond to that, and the key on the left is "Do". Put this together with Peter's clue, and you know that you need to step on the keys in the following order:

| ⊔ ⊔ | ⊔ ⊔ ⊔ |
|1| |2|4|3| | |
|5| |6| | | | |

If you do it correctly, the flames to the left of the organ will disappear. Note that it won't work if you didn't get the clue from Peter. If you make a mistake, you need to go outside and go back in to try again.

Explore the Underground

After the flames disappear, go down the stairs past where the flames were. Then go south and go down the stairs, then go to the southwest corner of the room and go west though the wall, and take the Big Heart. Then go back east to the previous room, then up the stairs.

From there, go south, and you will be outside again. Go west and enter the chapter 5 cave.