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Layer 3's danger is comparable to layer 4, but is similar in structure to layer 2. The Thermal Vents contains almost all of the most dangerous enemies in the Abyss, including the biome's mini-bosses.
As defeating Skeletron is required to open and loot these chests, it is highly recommended to explore these layers after Skeletron has been defeated. The islands on this layer have Ancient Treasure Chests containing either powerful late Pre-Hardmode weapons or useful items for further Abyss exploration.
The Murky Waters is the first true exploration site of the Abyss. No real danger is present in this layer, as it serves as a transition from the mostly peaceful Sulphurous Sea. The Sulphuric Depths form the entrance to the Abyss and are mostly safe, consisting of "islands" that generate in the middle and on the sides of the Abyss, with a few plants and decorations. The Abyss is divided into four distinct layers, each with a different set of tiles that generate and enemies that spawn. Because many enemies in the Abyss are initially passive, only becoming hostile when hit or when in close proximity to the player, stealthiness should be greatly prioritized while exploring the biome. It is extremely deep, dark, and perilous, filled with deadly enemies, which increase in strength as the biome grows deeper. It is located under the Sulphurous Sea on the Dungeon side of the world through a chasm on the seafloor. The Abyss is an aquatic biome added by the Calamity Mod which spawns upon world creation. "While there are many sightless crevasses in the deep sea, this one is a unique geological marvel." If you were looking for something other than the Abyss biome, see Abyss (disambiguation). The Abyss biome, as viewed on the map in a large world.