In real life, the Kremlin is a fortified complex which serves as residence for the current president of the Russian Federation. When the nuclear holocaust destroyed the known world, and Russia presumably fell apart, the Kremlin was abandoned by people; though something evil was left behind.
There is a rule among stalkers to never look at the Kremlin's stars, as they have a hypnotic effect. In the novel, Artyom reads (but barely understands) a book which interprets the Bolshevik red five-pointed star (and the similar WWII Allied white star) as a pentagram used to contain and control demons; the red stars of Kremlin, being the largest, contain the most powerful demons. This leads to a dream where he looks at the stars and feels an urge to go to them. Later, when he is accompanied by Miller to the surface, he looks at the stars, despite the warnings, and blacks out. In the videogame the player can look at the stars all day long and not be affected.
In the novel the station below the Kremlin is mentioned as a part of Metro 2. In this passage the Rangers, Artyom, and a young boy named Oleg are surprised by a strange fluid. This biomass emits some sort of psychic influence which causes a veteran stalker and, later, Oleg to wilfully jump in and be devoured by the organism. This creature was either killed when one of the stalkers threw a flamethrower canister at the creature and blew it up, causing it to quickly retreat. Months later, as said in Last Light, stalkers burned the creature in Kremlin, destroying it and its psychic influence. This means that the Kremlin's stars can now be looked at without the person being drawn into the building, and explains why the Kremlin is visited in Metro Last Light.
Although the specific organism isn't mentioned in the game, the biomass as seen in the videogame possibly serves as a replacement for the other biomass mentioned in the novel. In one of the journal pages in last light it says...
"For years nobody dared approach the Red Square. They said that something remained in the basement of the Kremlin, luring anything alive in and consuming it. Then the Order purged the Kremlin with fire... it's empty and all black with silt inside now. Just like the rest of the city. The Red Square. The stopped heart of a country long gone."
Metro Last LightEdit
In Metro Last Light Artyom visits the Red Square and Alexander Garden, which are situated near the Kremlin, on his way to Polis. He never, however, goes inside. Therefore its not known that the rumors about the Kremlin described in the novel is true or not.
- As heard in Market Station, the Kremlin was not meant to be destroyed, so it was attacked by a secret biological weapon instead, which might explain how the Kremlin Creature was created:
"The ones who fought during the war say the enemy didn't want to destroy the Kremlin, so, during the initial strike, they hit it with a secret Bioweapon. Nobody even noticed it first, they didn't even sound an alarm."
"By the time they realised what had happened, the weapon had already eaten everybody inside, and hundreds in the vicinity, too. So, today, the Kremlin still sits there, behind its walls, it's as though the apocalypse had never come."
- These lines are also said in a different way by Ulman in the novel Metro 2033, before the group of Stalkers reaches the Kremlin.
- In Metro: Last Light, however, the Kremlin is shown to have been damaged just as much as the rest of the city. (However this can be explained by natural decay and fire damage from when it was burned by Rangers)