|Metro Wiki has a video walkthrough for this level, Biomass (Level). See Biomass (Level)/Walkthrough.|
|“||Going down to the heart of the ancient citadel, I felt a chill in my soul. What man had the right to name himself the master of D6, and the devastating weapons it controlled?||„|
— Level description
The level starts with Artyom heading down the lift with Miller. Upon reaching the bottom, amoebae begin attacking the two Rangers. The following gauntlet is quite possibly one of the hardest parts of the game and it is advised that players be careful, as they can easily kill Artyom or Miller with only a few hits on higher difficulties.
After this the two will climb up into a small command chamber. After getting 1/4th power from the reactor, the biomass will attack. Miller then tells Artyom to run to the crane on the other side of the reactor chamber. The player must climb up the ladder and use the crane. The biomass is quite easy to disable if the player is quick enough to act, all that needs to be done is to run past the biomass when it's distracted by Miller. After it swings its tentacle, it is advised to run past it, run to the ladder, and climb it to access the crane.
From the crane, all the player has to do is guide the crane over the three reactor cells and lift them up. Speed is a necessity however, as the Biomass will try to attack the crane. Take note that the harder the difficulties, there is less time do it, as if the biomass hits the crane enough it will be destroyed and Artyom will die. It might take a few tries, as precision is require to activate all four before the crane is destroyed.
Once all four cells are lifted, the biomass will be too weakened to fight back, and all the player has to do is walk back to Miller and head to the surface. Care should still be given however, as even though the biomass is severely weakened by Artyom and Miller, it will still emit lethal doses of radiation.
The biomass cannot be killed but Miller has the intention of killing/destroying it "We'll be back to deal with this later, but first...[we'll deal with the dark ones]". After following Miller to the elevator a pseudo-cutscene will begin reflecting the power of D6, Miller's lust for the past, and the place of humanity.
- The biomass is radioactive, walking on or near it for too long can cause damage and even death.