Northern Underground World.
Eternal Night Dark Sea, the destination of countless underground dark rivers.
This boundless underground dark sea is divided by rock walls that hang down in layers, forming chambers of varying sizes.
Some of these chambers are so small that they cannot even accommodate a single boat.
Some chambers are vast, almost boundless, like a real sea.
The chambers of the dark sea are all interconnected at the bottom, where those water demonic beasts and fish swim freely in the lower layers of the dark sea.
If someone's swimming skills are as proficient as these aquatic creatures, they can perfectly start diving from the eastern sea of the Eternal Night Dark Sea and swim directly to the western seaside bordering the Obsidian Plain.
