Enter The Gungeon

Complete level 4 by killing the boss and going down the elevator 20 times. Don't be afraid of the quantity, the game is so difficult that you will go through the 4th hall much more than 20 times. You can open a shortcut to the level by completing a series of tasks for the NPC in the elevator shaft that you are freeing from prison. But it appears in the mine only after opening a short path to the 3rd floor (it is not necessary to return to the initial zone).