Underneath the Underworld

Underneath the Underworld is a Hardmode-only biome that can be accessed by digging all the way down the Underworld to reach "Rock Bottom", which will award you the achievement and allow you to go down to the undersides of the Underworld. It has harder enemies, more harsh hazards, and the best loot of Hardmode.

Enemies

 * Lava Elemental - 200 damage | On Fire! (5 secs), 600 HP, 20 DEF