Layer 2 is a dungeon found in the depths.
It has 2 floors that have unique enemies and bosses.
Floor 1 contains 1 mini boss & 1 main boss, floor 2 contains 1 main boss and is more difficult than floor 1.
Layer 2 contains some of he strongest items in the game such as "Ironsinger HeavyPlate", the "Kyrs" weapons, and powerful legendary weapons
Layer 2 is hard to learn at first but this video below will help you out alot: