The Sunken city is one of the ancient civilizations. It contains the same markings as found in some of Li's equipment, and is related to those found on the surface.
In the city, you need to find and escort the ghostly child to the center of the ruins.
It leads to the Boiler Room.
Within the Sunken City, you can farm some items:
- Near the first save crystal, you can obtain Sea Cake.
- In the first map, near the transition to the second map, you can collect plant leaves.
- In the second map, a breakable crate contains fish oil.