Here is the full list of all 9 ROAD HOMEWARD 3 underwater world achievements.
Swim to his house near the bridge and disembark.
Rise from the water.
Swim out of the cave.
Swim to the Park under water.
Swim to the city under water.
Swim through the old town and swim to the pipe.
Swim to the town in the old style.
Swim to the next level.
Start the game and swim a little.