Young Souls

Step 1- progress through the game until you get the second power Rune, making sure to free the armor vendor in the first dungeon level, the prison.

Step 2- in the third dungeon level with lava, continue straight to the right to fight a guardian for the golden key

Step 3- returning to the hub of the third dungeon level with level, enter the skull door in the bottom left. Fight the guardian at the end for the black knight armor.

Step 4- sell the armor to the armor vendor at the far right under the well in town. Buy it back, and repeat selling then buying until all three gold keeper achievements pop