This is a missable achievement
When you arrive at Valley of Dead you will be intruduced to large teleportaion crystals which are a purplish colour. These are called minnims.
At the bottom of the area to the left of the two huge statues look for a minnum which is dark red and different. You will be told that unlike the others this one has no end destination. Go through all the dialogue options.
Now travel to the top of the area just past Tantalum and you will see a second. Again you are told the minnim is dying.
Choose the option, 'Step closer, Expel whatever is trying to get out of your body
Your body expels a dark sludge which heals and reactivates both crystals, and unlocks the achievement.
Edit: If the second minnim is not there try going into necropolis then returning - thanks to Risseless for update