Underground Ocean

The  is a large body of water that is very deep underground at the bottom of a large chain of caverns. There are certain monsters that spawn in this location such as Black Tiger Fish and Black Bat.

The significance to this area of the world, is that it is the only place where you can find the Shark, which drop an otherwise unique to obtain resource, the Shark Fish Skin. To reach the Subterranean Lake one should take precautions before attempting a drop into this cavern as it'll more than likely require the use of a Teleporter or a built tower to escape.

The surroundings are mainly composed of Granite along the floor, Water filling up a fixed percentage of the cavern chains, with the Stone from the ceiling and above heading straight up.

Mad Crab
The Mad Crab can be found west of the hole after the Chasm. The area where you fight the Mad Crab is raised above the water level, preventing flooding and allowing you to have a good arena to fight him in.

Bosses

 * Mad Crab

Monsters

 * Black Bat
 * Black Tiger Fish
 * Tiger Fish
 * Shark

Environment

 * Aluminum
 * Coal Ore
 * Coral
 * Flower of Light
 * Granite
 * Iron
 * Stone
 * Uranium
 * Water
 * Water Tree Log