How do they get to VV3 in the first place, maybe they were swimming out in the ocean when a wave came and swept them out, when they got back to shore they were in a new, very strange part of the island.

Maybe one day as a villager was admiring the gongs casing, she saw light behind it. She and her baby ventured down a passageway and came out in a cave leading to vv3 map.

They could clmb up the waterfall and follow the stream.