The reason it's 120 mb is that the world is unintentionally built too big. The actual adventure didn't even need/used that much space in the game's world. I ended up exploring the city and jellyfish fields out of curiosity for what seemed like 30 minutes. There was no vehicle and everything had to be done from sprinting alone. I don't know why King Neptune is at spawn. And I don't think this has an ending.
This game isn't that bad :)