In this video guide I will show you how to destroy all 4 soul caches in the Slag Pit. So this will be the second level in the game. What you are looking for is blue orbs hovering in the air. You will need to kill all the enemies near them for it to turn red. Once it turns red, you will be able to shoot the orb with Strife to claim it. For better details on where they are please watch the video. Once you destroy the fourth after killing the enemies near it the achievement will pop.