Gore Nests are demonic obstacles in Doom (2016). They are portals from Hell to Mars that have to be cleared to remove lockdowns of certain areas in the game. They are often lightly guarded (if at all), but taking one out calls in more demons from Hell.
Gore Nests return in Doom Eternal, although they are mostly used as the entryways for the Slayer Gates and Secret Encounters in the base game and The Ancient Gods - Part One; the former has purple portals and the latter has magenta portals instead of red ones. Completing each secret encounter in a level in TAG1 will reward the player with a new skin for the Doom slayer. Secret encounters are timed, and if the player fails they'd have to retry it. The game also features a Super Gore Nest, an enormous version of the Gore Nest that can summon entire legions at once. The origin point of Hell's incursion on Earth, it serves as a level unto itself when the Doom Slayer travels through it in an attempt to destroy it.
In The Ancient Gods - Part Two, Gore Nest with yellow portals serve as the triggers for Escalation Encounters. When destroyed, they summon a massive horde of powerful demons that must be slain to progress; doing so also unlocks an upgrade for the Sentinel Hammer. However, the Gore Nest will also respawn in its original location; destroying it a second and final time will trigger an even harder battle that rewards the player with a new skin for the Doom Slayer if they emerge victorious, much like the secret encounters in TAG1.
Studies of demons upon entering this dimension have shown that their conduct is not purely vindictive - there is a method behind their actions. When a demon captures their prey, the fresh kill is taken to a temporary ceremonial site where arcane rituals are performed on the pile of blood and gore.
When enough corpses have been gathered, the ceremonial site becomes a "Gore Nest". These sites, imbued with Hell energy from the rituals, act as umbilical cords to Hell. Extreme caution must be taken when approaching a Gore Nest. Attacking the nest, or indeed any demons within close proximity to the nest, will act as an alarm and siphon more demons from Hell.
Gore Nests appear to actually be a sessile animal organism somewhat like a coral reef, resembling a dinosaur-like head with a large open mouth lined with teeth. Above the "mouth" lies a large, spherical portal - the default color seems to be red, but other colors are known to exist. Skulls and other body parts provide the underlying material for the "reef." On the right side of the Gore Nest's "head" is a large yellow pustule which looks like it might be the creature's eye; this pustule encases a vital organ similar to a heart. The Gore Nest also whispers loudly and ominously, and this noise is often the first sign the player has that there is one nearby.
The Mancubus has a similar organ to that of the Gore Nest within its chest, visible when the player performs a Glory Kill on it, which suggests that it is in fact a heart in the animal sense, even looking somewhat like a human heart with three large yellow pustules on it.
Gore Nests themselves are completely harmless; to destroy them, the player simply needs to approach and interact with them. This causes the Doom Slayer to punch through the Gore Nest's large pustule and rip out its "heart"; a few seconds later, the Gore Nest will explode into the piles of flesh and gore it was made of. Unfortunately, it also lets out a piercingly loud scream that serves as a distress signal, and a task force from Hell will warp into the area to deal with the threat.