The Coal Pits is the second biome on the main path, located directly below the Mines.
The theme that plays within the Coal Pits is Liekkiö.
The Coal Pits consists mostly of wide open passages composed of thick sections composed of coal vein and rock, with wooden beams blocking off certain areas or providing platforms to stand on. The long tunnels are frequently dead ends which necessitates lots of backtracking to progress further, unless digging or explosives are used. Gold deposits litter the terrain which can be dug out with suitable spells (Chainsaw, Digging Bolt, Energy Orb, etc). Note that coal vein is much easier to dig through than grey rock. Deep pools of water and pools of toxic sludge are also abundant. Because the biome has no "safety room" present in later biomes, it is possible for pools of toxic sludge to generate directly under the Holy Mountain exit. Wooden Mining machinery can occasionally be spotted, serving no functional purpose.
While more open than the Mines, enemy conflicts can frequently make large areas hazardous, with frequently appearing Slimes, toxic sludge tanks, and pools of sludge mixing with lava bled by Fireflies to create unpurifiable toxic rock and gas. Sea mines also make their first appearance here as well as easily ignited vats of gunpowder.
The Coal pits feature several new creatures as well as other types of Hiisi, including:
A metal capsule-shaped structure will sometimes appear, with a small pool of Water in the bottom. Emblazoned on the inside of the capsule is the alchemical symbol of Water, the downward-pointed triangle, and an image of a cloud is etched into the ceiling of the capsule.